[v4] x86/p2m: use large pages for MMIO mappings

Commit Message

Jan Beulich Jan. 22, 2016, 3:42 p.m. UTC

When mapping large BARs (e.g. the frame buffer of a graphics card) the
overhead of establishing such mappings using only 4k pages has,
particularly after the XSA-125 fix, become unacceptable. Alter the
XEN_DOMCTL_memory_mapping semantics once again, so that there's no
longer a fixed amount of guest frames that represents the upper limit
of what a single invocation can map. Instead bound execution time by
limiting the number of iterations (regardless of page size).

Signed-off-by: Jan Beulich <[e-mail]>
---
Open issues (perhaps for subsequent changes):
- ARM side unimplemented (and hence libxc for now made cope with both
  models), the main issue (besides my inability to test any change
  there) being the many internal uses of map_mmio_regions())
- iommu_{,un}map_page() interfaces don't support "order" (hence
  mmio_order() for now returns zero when !iommu_hap_pt_share, which in
  particular means the AMD side isn't being taken care of just yet, but
  note that this also has the intended effect of suppressing non-zero
  order mappings in the shadow mode case)
---
v4: Move cleanup duty entirely to the caller of the hypercall. Move
    return value description to from commit message to domctl.h.
v3: Re-base on top of "x86/hvm: fold opt_hap_{2mb,1gb} into
    hap_capabilities". Extend description to spell out new return value
    meaning. Add a couple of code comments. Use PAGE_ORDER_4K instead
    of literal 0. Take into consideration r/o MMIO pages.
v2: Produce valid entries for large p2m_mmio_direct mappings in
    p2m_pt_set_entry(). Don't open code iommu_use_hap_pt() in
    mmio_order(). Update function comment of set_typed_p2m_entry() and
    clear_mmio_p2m_entry(). Use PRI_mfn. Add ASSERT()s to
    {,un}map_mmio_regions() to detect otherwise endless loops.
x86/p2m: use large pages for MMIO mappings

When mapping large BARs (e.g. the frame buffer of a graphics card) the
overhead of establishing such mappings using only 4k pages has,
particularly after the XSA-125 fix, become unacceptable. Alter the
XEN_DOMCTL_memory_mapping semantics once again, so that there's no
longer a fixed amount of guest frames that represents the upper limit
of what a single invocation can map. Instead bound execution time by
limiting the number of iterations (regardless of page size).

Signed-off-by: Jan Beulich <[e-mail]>
---
Open issues (perhaps for subsequent changes):
- ARM side unimplemented (and hence libxc for now made cope with both
  models), the main issue (besides my inability to test any change
  there) being the many internal uses of map_mmio_regions())
- iommu_{,un}map_page() interfaces don't support "order" (hence
  mmio_order() for now returns zero when !iommu_hap_pt_share, which in
  particular means the AMD side isn't being taken care of just yet, but
  note that this also has the intended effect of suppressing non-zero
  order mappings in the shadow mode case)
---
v4: Move cleanup duty entirely to the caller of the hypercall. Move
    return value description to from commit message to domctl.h.
v3: Re-base on top of "x86/hvm: fold opt_hap_{2mb,1gb} into
    hap_capabilities". Extend description to spell out new return value
    meaning. Add a couple of code comments. Use PAGE_ORDER_4K instead
    of literal 0. Take into consideration r/o MMIO pages.
v2: Produce valid entries for large p2m_mmio_direct mappings in
    p2m_pt_set_entry(). Don't open code iommu_use_hap_pt() in
    mmio_order(). Update function comment of set_typed_p2m_entry() and
    clear_mmio_p2m_entry(). Use PRI_mfn. Add ASSERT()s to
    {,un}map_mmio_regions() to detect otherwise endless loops.

--- a/tools/libxc/xc_domain.c
+++ b/tools/libxc/xc_domain.c
@@ -2174,7 +2174,7 @@ int xc_domain_memory_mapping(
 {
     DECLARE_DOMCTL;
     xc_dominfo_t info;
-    int ret = 0, err;
+    int ret = 0, rc;
     unsigned long done = 0, nr, max_batch_sz;
 
     if ( xc_domain_getinfo(xch, domid, 1, &info) != 1 ||
@@ -2199,19 +2199,24 @@ int xc_domain_memory_mapping(
         domctl.u.memory_mapping.nr_mfns = nr;
         domctl.u.memory_mapping.first_gfn = first_gfn + done;
         domctl.u.memory_mapping.first_mfn = first_mfn + done;
-        err = do_domctl(xch, &domctl);
-        if ( err && errno == E2BIG )
+        rc = do_domctl(xch, &domctl);
+        if ( rc < 0 && errno == E2BIG )
         {
             if ( max_batch_sz <= 1 )
                 break;
             max_batch_sz >>= 1;
             continue;
         }
+        if ( rc > 0 )
+        {
+            done += rc;
+            continue;
+        }
         /* Save the first error... */
         if ( !ret )
-            ret = err;
+            ret = rc;
         /* .. and ignore the rest of them when removing. */
-        if ( err && add_mapping != DPCI_REMOVE_MAPPING )
+        if ( rc && add_mapping != DPCI_REMOVE_MAPPING )
             break;
 
         done += nr;
--- a/xen/arch/x86/domain_build.c
+++ b/xen/arch/x86/domain_build.c
@@ -436,7 +436,8 @@ static __init void pvh_add_mem_mapping(s
         else
             a = p2m_access_rw;
 
-        if ( (rc = set_mmio_p2m_entry(d, gfn + i, _mfn(mfn + i), a)) )
+        if ( (rc = set_mmio_p2m_entry(d, gfn + i, _mfn(mfn + i),
+                                      PAGE_ORDER_4K, a)) )
             panic("pvh_add_mem_mapping: gfn:%lx mfn:%lx i:%ld rc:%d\n",
                   gfn, mfn, i, rc);
         if ( !(i & 0xfffff) )
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2491,7 +2491,7 @@ static int vmx_alloc_vlapic_mapping(stru
     share_xen_page_with_guest(pg, d, XENSHARE_writable);
     d->arch.hvm_domain.vmx.apic_access_mfn = mfn;
     set_mmio_p2m_entry(d, paddr_to_pfn(APIC_DEFAULT_PHYS_BASE), _mfn(mfn),
-                       p2m_get_hostp2m(d)->default_access);
+                       PAGE_ORDER_4K, p2m_get_hostp2m(d)->default_access);
 
     return 0;
 }
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -899,48 +899,62 @@ void p2m_change_type_range(struct domain
     p2m_unlock(p2m);
 }
 
-/* Returns: 0 for success, -errno for failure */
+/*
+ * Returns:
+ *    0        for success
+ *    -errno   for failure
+ *    order+1  for caller to retry with order (guaranteed smaller than
+ *             the order value passed in)
+ */
 static int set_typed_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
-                               p2m_type_t gfn_p2mt, p2m_access_t access)
+                               unsigned int order, p2m_type_t gfn_p2mt,
+                               p2m_access_t access)
 {
     int rc = 0;
     p2m_access_t a;
     p2m_type_t ot;
     mfn_t omfn;
+    unsigned int cur_order = 0;
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
 
     if ( !paging_mode_translate(d) )
         return -EIO;
 
-    gfn_lock(p2m, gfn, 0);
-    omfn = p2m->get_entry(p2m, gfn, &ot, &a, 0, NULL, NULL);
+    gfn_lock(p2m, gfn, order);
+    omfn = p2m->get_entry(p2m, gfn, &ot, &a, 0, &cur_order, NULL);
+    if ( cur_order < order )
+    {
+        gfn_unlock(p2m, gfn, order);
+        return cur_order + 1;
+    }
     if ( p2m_is_grant(ot) || p2m_is_foreign(ot) )
     {
-        gfn_unlock(p2m, gfn, 0);
+        gfn_unlock(p2m, gfn, order);
         domain_crash(d);
         return -ENOENT;
     }
     else if ( p2m_is_ram(ot) )
     {
+        unsigned long i;
+
         ASSERT(mfn_valid(omfn));
-        set_gpfn_from_mfn(mfn_x(omfn), INVALID_M2P_ENTRY);
+        for ( i = 0; i < (1UL << order); ++i )
+            set_gpfn_from_mfn(mfn_x(omfn) + i, INVALID_M2P_ENTRY);
     }
 
     P2M_DEBUG("set %d %lx %lx\n", gfn_p2mt, gfn, mfn_x(mfn));
-    rc = p2m_set_entry(p2m, gfn, mfn, PAGE_ORDER_4K, gfn_p2mt,
-                       access);
+    rc = p2m_set_entry(p2m, gfn, mfn, order, gfn_p2mt, access);
     if ( rc )
-        gdprintk(XENLOG_ERR,
-                 "p2m_set_entry failed! mfn=%08lx rc:%d\n",
-                 mfn_x(get_gfn_query_unlocked(p2m->domain, gfn, &ot)), rc);
+        gdprintk(XENLOG_ERR, "p2m_set_entry: %#lx:%u -> %d (0x%"PRI_mfn")\n",
+                 gfn, order, rc, mfn_x(mfn));
     else if ( p2m_is_pod(ot) )
     {
         pod_lock(p2m);
-        p2m->pod.entry_count--;
+        p2m->pod.entry_count -= 1UL << order;
         BUG_ON(p2m->pod.entry_count < 0);
         pod_unlock(p2m);
     }
-    gfn_unlock(p2m, gfn, 0);
+    gfn_unlock(p2m, gfn, order);
 
     return rc;
 }
@@ -949,14 +963,21 @@ static int set_typed_p2m_entry(struct do
 static int set_foreign_p2m_entry(struct domain *d, unsigned long gfn,
                                  mfn_t mfn)
 {
-    return set_typed_p2m_entry(d, gfn, mfn, p2m_map_foreign,
+    return set_typed_p2m_entry(d, gfn, mfn, PAGE_ORDER_4K, p2m_map_foreign,
                                p2m_get_hostp2m(d)->default_access);
 }
 
 int set_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
-                       p2m_access_t access)
+                       unsigned int order, p2m_access_t access)
 {
-    return set_typed_p2m_entry(d, gfn, mfn, p2m_mmio_direct, access);
+    if ( order &&
+         rangeset_overlaps_range(mmio_ro_ranges, mfn_x(mfn),
+                                 mfn_x(mfn) + (1UL << order) - 1) &&
+         !rangeset_contains_range(mmio_ro_ranges, mfn_x(mfn),
+                                  mfn_x(mfn) + (1UL << order) - 1) )
+        return order;
+
+    return set_typed_p2m_entry(d, gfn, mfn, order, p2m_mmio_direct, access);
 }
 
 int set_identity_p2m_entry(struct domain *d, unsigned long gfn,
@@ -1009,20 +1030,33 @@ int set_identity_p2m_entry(struct domain
     return ret;
 }
 
-/* Returns: 0 for success, -errno for failure */
-int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn)
+/*
+ * Returns:
+ *    0        for success
+ *    -errno   for failure
+ *    order+1  for caller to retry with order (guaranteed smaller than
+ *             the order value passed in)
+ */
+int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
+                         unsigned int order)
 {
     int rc = -EINVAL;
     mfn_t actual_mfn;
     p2m_access_t a;
     p2m_type_t t;
+    unsigned int cur_order = 0;
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
 
     if ( !paging_mode_translate(d) )
         return -EIO;
 
-    gfn_lock(p2m, gfn, 0);
-    actual_mfn = p2m->get_entry(p2m, gfn, &t, &a, 0, NULL, NULL);
+    gfn_lock(p2m, gfn, order);
+    actual_mfn = p2m->get_entry(p2m, gfn, &t, &a, 0, &cur_order, NULL);
+    if ( cur_order < order )
+    {
+        rc = cur_order + 1;
+        goto out;
+    }
 
     /* Do not use mfn_valid() here as it will usually fail for MMIO pages. */
     if ( (INVALID_MFN == mfn_x(actual_mfn)) || (t != p2m_mmio_direct) )
@@ -1035,11 +1069,11 @@ int clear_mmio_p2m_entry(struct domain *
         gdprintk(XENLOG_WARNING,
                  "no mapping between mfn %08lx and gfn %08lx\n",
                  mfn_x(mfn), gfn);
-    rc = p2m_set_entry(p2m, gfn, _mfn(INVALID_MFN), PAGE_ORDER_4K, p2m_invalid,
+    rc = p2m_set_entry(p2m, gfn, _mfn(INVALID_MFN), order, p2m_invalid,
                        p2m->default_access);
 
  out:
-    gfn_unlock(p2m, gfn, 0);
+    gfn_unlock(p2m, gfn, order);
 
     return rc;
 }
@@ -2095,6 +2129,25 @@ void *map_domain_gfn(struct p2m_domain *
     return map_domain_page(*mfn);
 }
 
+static unsigned int mmio_order(const struct domain *d,
+                               unsigned long start_fn, unsigned long nr)
+{
+    if ( !need_iommu(d) || !iommu_use_hap_pt(d) ||
+         (start_fn & ((1UL << PAGE_ORDER_2M) - 1)) || !(nr >> PAGE_ORDER_2M) )
+        return 0;
+
+    if ( !(start_fn & ((1UL << PAGE_ORDER_1G) - 1)) && (nr >> PAGE_ORDER_1G) &&
+         hap_has_1gb )
+        return PAGE_ORDER_1G;
+
+    if ( hap_has_2mb )
+        return PAGE_ORDER_2M;
+
+    return 0;
+}
+
+#define MAP_MMIO_MAX_ITER 64 /* pretty arbitrary */
+
 int map_mmio_regions(struct domain *d,
                      unsigned long start_gfn,
                      unsigned long nr,
@@ -2102,22 +2155,29 @@ int map_mmio_regions(struct domain *d,
 {
     int ret = 0;
     unsigned long i;
+    unsigned int iter, order;
 
     if ( !paging_mode_translate(d) )
         return 0;
 
-    for ( i = 0; !ret && i < nr; i++ )
+    for ( iter = i = 0; i < nr && iter < MAP_MMIO_MAX_ITER;
+          i += 1UL << order, ++iter )
     {
-        ret = set_mmio_p2m_entry(d, start_gfn + i, _mfn(mfn + i),
-                                 p2m_get_hostp2m(d)->default_access);
-        if ( ret )
+        /* OR'ing gfn and mfn values will return an order suitable to both. */
+        for ( order = mmio_order(d, (start_gfn + i) | (mfn + i), nr - i); ;
+              order = ret - 1 )
         {
-            unmap_mmio_regions(d, start_gfn, i, mfn);
-            break;
+            ret = set_mmio_p2m_entry(d, start_gfn + i, _mfn(mfn + i), order,
+                                     p2m_get_hostp2m(d)->default_access);
+            if ( ret <= 0 )
+                break;
+            ASSERT(ret <= order);
         }
+        if ( ret < 0 )
+            break;
     }
 
-    return ret;
+    return i == nr ? 0 : i ?: ret;
 }
 
 int unmap_mmio_regions(struct domain *d,
@@ -2125,20 +2185,30 @@ int unmap_mmio_regions(struct domain *d,
                        unsigned long nr,
                        unsigned long mfn)
 {
-    int err = 0;
+    int ret = 0;
     unsigned long i;
+    unsigned int iter, order;
 
     if ( !paging_mode_translate(d) )
         return 0;
 
-    for ( i = 0; i < nr; i++ )
+    for ( iter = i = 0; i < nr && iter < MAP_MMIO_MAX_ITER;
+          i += 1UL << order, ++iter )
     {
-        int ret = clear_mmio_p2m_entry(d, start_gfn + i, _mfn(mfn + i));
-        if ( ret )
-            err = ret;
+        /* OR'ing gfn and mfn values will return an order suitable to both. */
+        for ( order = mmio_order(d, (start_gfn + i) | (mfn + i), nr - i); ;
+              order = ret - 1 )
+        {
+            ret = clear_mmio_p2m_entry(d, start_gfn + i, _mfn(mfn + i), order);
+            if ( ret <= 0 )
+                break;
+            ASSERT(ret <= order);
+        }
+        if ( ret < 0 )
+            break;
     }
 
-    return err;
+    return i == nr ? 0 : i ?: ret;
 }
 
 unsigned int p2m_find_altp2m_by_eptp(struct domain *d, uint64_t eptp)
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -136,6 +136,7 @@ static void ept_p2m_type_to_flags(struct
             entry->r = entry->x = 1;
             entry->w = !rangeset_contains_singleton(mmio_ro_ranges,
                                                     entry->mfn);
+            ASSERT(entry->w || !is_epte_superpage(entry));
             entry->a = !!cpu_has_vmx_ept_ad;
             entry->d = entry->w && cpu_has_vmx_ept_ad;
             break;
--- a/xen/arch/x86/mm/p2m-pt.c
+++ b/xen/arch/x86/mm/p2m-pt.c
@@ -72,7 +72,8 @@ static const unsigned long pgt[] = {
     PGT_l3_page_table
 };
 
-static unsigned long p2m_type_to_flags(p2m_type_t t, mfn_t mfn)
+static unsigned long p2m_type_to_flags(p2m_type_t t, mfn_t mfn,
+                                       unsigned int level)
 {
     unsigned long flags;
     /*
@@ -107,6 +108,8 @@ static unsigned long p2m_type_to_flags(p
     case p2m_mmio_direct:
         if ( !rangeset_contains_singleton(mmio_ro_ranges, mfn_x(mfn)) )
             flags |= _PAGE_RW;
+        else
+            ASSERT(!level);
         return flags | P2M_BASE_FLAGS | _PAGE_PCD;
     }
 }
@@ -436,7 +439,7 @@ static int do_recalc(struct p2m_domain *
             p2m_type_t p2mt = p2m_is_logdirty_range(p2m, gfn & mask, gfn | ~mask)
                               ? p2m_ram_logdirty : p2m_ram_rw;
             unsigned long mfn = l1e_get_pfn(e);
-            unsigned long flags = p2m_type_to_flags(p2mt, _mfn(mfn));
+            unsigned long flags = p2m_type_to_flags(p2mt, _mfn(mfn), level);
 
             if ( level )
             {
@@ -573,7 +576,7 @@ p2m_pt_set_entry(struct p2m_domain *p2m,
         ASSERT(!mfn_valid(mfn) || p2mt != p2m_mmio_direct);
         l3e_content = mfn_valid(mfn) || p2m_allows_invalid_mfn(p2mt)
             ? l3e_from_pfn(mfn_x(mfn),
-                           p2m_type_to_flags(p2mt, mfn) | _PAGE_PSE)
+                           p2m_type_to_flags(p2mt, mfn, 2) | _PAGE_PSE)
             : l3e_empty();
         entry_content.l1 = l3e_content.l3;
 
@@ -609,7 +612,7 @@ p2m_pt_set_entry(struct p2m_domain *p2m,
 
         if ( mfn_valid(mfn) || p2m_allows_invalid_mfn(p2mt) )
             entry_content = p2m_l1e_from_pfn(mfn_x(mfn),
-                                             p2m_type_to_flags(p2mt, mfn));
+                                             p2m_type_to_flags(p2mt, mfn, 0));
         else
             entry_content = l1e_empty();
 
@@ -645,7 +648,7 @@ p2m_pt_set_entry(struct p2m_domain *p2m,
         ASSERT(!mfn_valid(mfn) || p2mt != p2m_mmio_direct);
         if ( mfn_valid(mfn) || p2m_allows_invalid_mfn(p2mt) )
             l2e_content = l2e_from_pfn(mfn_x(mfn),
-                                       p2m_type_to_flags(p2mt, mfn) |
+                                       p2m_type_to_flags(p2mt, mfn, 1) |
                                        _PAGE_PSE);
         else
             l2e_content = l2e_empty();
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -1046,10 +1046,12 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xe
              (gfn + nr_mfns - 1) < gfn ) /* wrap? */
             break;
 
+#ifndef CONFIG_X86 /* XXX ARM!? */
         ret = -E2BIG;
         /* Must break hypercall up as this could take a while. */
         if ( nr_mfns > 64 )
             break;
+#endif
 
         ret = -EPERM;
         if ( !iomem_access_permitted(current->domain, mfn, mfn_end) ||
@@ -1067,7 +1069,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xe
                    d->domain_id, gfn, mfn, nr_mfns);
 
             ret = map_mmio_regions(d, gfn, nr_mfns, mfn);
-            if ( ret )
+            if ( ret < 0 )
                 printk(XENLOG_G_WARNING
                        "memory_map:fail: dom%d gfn=%lx mfn=%lx nr=%lx ret:%ld\n",
                        d->domain_id, gfn, mfn, nr_mfns, ret);
@@ -1079,7 +1081,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xe
                    d->domain_id, gfn, mfn, nr_mfns);
 
             ret = unmap_mmio_regions(d, gfn, nr_mfns, mfn);
-            if ( ret && is_hardware_domain(current->domain) )
+            if ( ret < 0 && is_hardware_domain(current->domain) )
                 printk(XENLOG_ERR
                        "memory_map: error %ld removing dom%d access to [%lx,%lx]\n",
                        ret, d->domain_id, mfn, mfn_end);
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -259,7 +259,7 @@ int guest_remove_page(struct domain *d,
     }
     if ( p2mt == p2m_mmio_direct )
     {
-        clear_mmio_p2m_entry(d, gmfn, _mfn(mfn));
+        clear_mmio_p2m_entry(d, gmfn, _mfn(mfn), 0);
         put_gfn(d, gmfn);
         return 1;
     }
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -574,8 +574,9 @@ int p2m_is_logdirty_range(struct p2m_dom
 
 /* Set mmio addresses in the p2m table (for pass-through) */
 int set_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
-                       p2m_access_t access);
-int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn);
+                       unsigned int order, p2m_access_t access);
+int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
+                         unsigned int order);
 
 /* Set identity addresses in the p2m table (for pass-through) */
 int set_identity_p2m_entry(struct domain *d, unsigned long gfn,
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -542,8 +542,14 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_bind_
 
 
 /* Bind machine I/O address range -> HVM address range. */
-/* If this returns -E2BIG lower nr_mfns value. */
 /* XEN_DOMCTL_memory_mapping */
+/* Returns
+   - zero     (success, everything done)
+   - -E2BIG   (passed in nr_mfns value too large for the implementation)
+   - positive (partial success, this many [less than nr_mfns] done,
+               requiring re-invocation by the caller with updated inputs)
+   - negative (error)
+*/
 #define DPCI_ADD_MAPPING         1
 #define DPCI_REMOVE_MAPPING      0
 struct xen_domctl_memory_mapping {

Comments

Ian Campbell Jan. 25, 2016, 12:16 p.m. UTC | #1

On Fri, 2016-01-22 at 08:42 -0700, Jan Beulich wrote:
> When mapping large BARs (e.g. the frame buffer of a graphics card) the
> overhead of establishing such mappings using only 4k pages has,
> particularly after the XSA-125 fix, become unacceptable. Alter the
> XEN_DOMCTL_memory_mapping semantics once again, so that there's no
> longer a fixed amount of guest frames that represents the upper limit
> of what a single invocation can map. Instead bound execution time by
> limiting the number of iterations (regardless of page size).
> 
> Signed-off-by: Jan Beulich <[e-mail]>
> ---
> Open issues (perhaps for subsequent changes):
> - ARM side unimplemented (and hence libxc for now made cope with both
>   models), the main issue (besides my inability to test any change
>   there) being the many internal uses of map_mmio_regions())
> - iommu_{,un}map_page() interfaces don't support "order" (hence
>   mmio_order() for now returns zero when !iommu_hap_pt_share, which in
>   particular means the AMD side isn't being taken care of just yet, but
>   note that this also has the intended effect of suppressing non-zero
>   order mappings in the shadow mode case)
> ---
> v4: Move cleanup duty entirely to the caller of the hypercall. Move
>     return value description to from commit message to domctl.h.
> v3: Re-base on top of "x86/hvm: fold opt_hap_{2mb,1gb} into
>     hap_capabilities". Extend description to spell out new return value
>     meaning. Add a couple of code comments. Use PAGE_ORDER_4K instead
>     of literal 0. Take into consideration r/o MMIO pages.
> v2: Produce valid entries for large p2m_mmio_direct mappings in
>     p2m_pt_set_entry(). Don't open code iommu_use_hap_pt() in
>     mmio_order(). Update function comment of set_typed_p2m_entry() and
>     clear_mmio_p2m_entry(). Use PRI_mfn. Add ASSERT()s to
>     {,un}map_mmio_regions() to detect otherwise endless loops.
> 
> --- a/tools/libxc/xc_domain.c
> +++ b/tools/libxc/xc_domain.c
> @@ -2174,7 +2174,7 @@ int xc_domain_memory_mapping(
>  {
>      DECLARE_DOMCTL;
>      xc_dominfo_t info;
> -    int ret = 0, err;
> +    int ret = 0, rc;
>      unsigned long done = 0, nr, max_batch_sz;
>  
>      if ( xc_domain_getinfo(xch, domid, 1, &info) != 1 ||
> @@ -2199,19 +2199,24 @@ int xc_domain_memory_mapping(
>          domctl.u.memory_mapping.nr_mfns = nr;
>          domctl.u.memory_mapping.first_gfn = first_gfn + done;
>          domctl.u.memory_mapping.first_mfn = first_mfn + done;
> -        err = do_domctl(xch, &domctl);
> -        if ( err && errno == E2BIG )
> +        rc = do_domctl(xch, &domctl);
> +        if ( rc < 0 && errno == E2BIG )
>          {
>              if ( max_batch_sz <= 1 )
>                  break;
>              max_batch_sz >>= 1;
>              continue;
>          }
> +        if ( rc > 0 )
> +        {
> +            done += rc;
> +            continue;
> +        }
>          /* Save the first error... */
>          if ( !ret )
> -            ret = err;
> +            ret = rc;
>          /* .. and ignore the rest of them when removing. */
> -        if ( err && add_mapping != DPCI_REMOVE_MAPPING )
> +        if ( rc && add_mapping != DPCI_REMOVE_MAPPING )
>              break;

This all looks good to me, assuming I've interpreted the interface comment
correctly.

> +
> +#define MAP_MMIO_MAX_ITER 64 /* pretty arbitrary */
> +

I suppose no existing in-tree code exceeds that (or there'd be more patch
here).

64 seems like as good a number as anything (corresponds to 256K for 4K
mappings, which doesn't seem too low).
 
>          done += nr;
> --- a/xen/include/public/domctl.h
> +++ b/xen/include/public/domctl.h
> @@ -542,8 +542,14 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_bind_
>  
>  
>  /* Bind machine I/O address range -> HVM address range. */
> -/* If this returns -E2BIG lower nr_mfns value. */
>  /* XEN_DOMCTL_memory_mapping */
> +/* Returns
> +   - zero     (success, everything done)
> +   - -E2BIG   (passed in nr_mfns value too large for the implementation)
> +   - positive (partial success, this many [less than nr_mfns] done,

Is the successful region contiguous, i.e. 0..return val, or does the caller
need to figure it somehow? (I think based on libxc changes the former, but
it should be spelt out here I think).



> +               requiring re-invocation by the caller with updated inputs)
> +   - negative (error)

This is a more general case of -E2BIG, you might fix that by saying "other
error" or by moving -E2BIG to be a subclause.

Jan Beulich Jan. 25, 2016, 1:54 p.m. UTC | #2

>>> On 25.01.16 at 13:16, <[e-mail]> wrote:
> On Fri, 2016-01-22 at 08:42 -0700, Jan Beulich wrote:
>> +#define MAP_MMIO_MAX_ITER 64 /* pretty arbitrary */
>> +
> 
> I suppose no existing in-tree code exceeds that (or there'd be more patch
> here).

There simply is no in-tree user other than the domctl on x86. It's
only ARM which has numerous other users (complicating the fixing
of the issue there).

>> --- a/xen/include/public/domctl.h
>> +++ b/xen/include/public/domctl.h
>> @@ -542,8 +542,14 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_bind_
>>  
>>  
>>  /* Bind machine I/O address range -> HVM address range. */
>> -/* If this returns -E2BIG lower nr_mfns value. */
>>  /* XEN_DOMCTL_memory_mapping */
>> +/* Returns
>> +   - zero     (success, everything done)
>> +   - -E2BIG   (passed in nr_mfns value too large for the implementation)
>> +   - positive (partial success, this many [less than nr_mfns] done,
> 
> Is the successful region contiguous, i.e. 0..return val, or does the caller
> need to figure it somehow? (I think based on libxc changes the former, but
> it should be spelt out here I think).

Yes, it is contiguous, but I'm at a loss how to spell out the (seemingly
obvious) fact here: "partial success, this many [less than nr_mfns]
initial iterations done" doesn't sound much better to me. Everything
else I can think of would require a full second sentence, which I
wouldn't like here.

>> +               requiring re-invocation by the caller with updated inputs)
>> +   - negative (error)
> 
> This is a more general case of -E2BIG, you might fix that by saying "other
> error" or by moving -E2BIG to be a subclause.

"other error" would seem okay, or how about "negative (error; other
than -E2BIG)"?

Jan

Ian Campbell Jan. 25, 2016, 2:05 p.m. UTC | #3

On Mon, 2016-01-25 at 06:54 -0700, Jan Beulich wrote:
> > > > On 25.01.16 at 13:16, <[e-mail]> wrote:
> > On Fri, 2016-01-22 at 08:42 -0700, Jan Beulich wrote:
> > > +#define MAP_MMIO_MAX_ITER 64 /* pretty arbitrary */
> > > +
> > 
> > I suppose no existing in-tree code exceeds that (or there'd be more
> > patch
> > here).
> 
> There simply is no in-tree user other than the domctl on x86.


Right, I meant callers of the domctl (via libxc)

>  It's
> only ARM which has numerous other users (complicating the fixing
> of the issue there).
> 
> > > --- a/xen/include/public/domctl.h
> > > +++ b/xen/include/public/domctl.h
> > > @@ -542,8 +542,14 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_bind_
> > >  
> > >  
> > >  /* Bind machine I/O address range -> HVM address range. */
> > > -/* If this returns -E2BIG lower nr_mfns value. */
> > >  /* XEN_DOMCTL_memory_mapping */
> > > +/* Returns
> > > +   - zero     (success, everything done)
> > > +   - -E2BIG   (passed in nr_mfns value too large for the
> > > implementation)
> > > +   - positive (partial success, this many [less than nr_mfns] done,
> > 
> > Is the successful region contiguous, i.e. 0..return val, or does the
> > caller
> > need to figure it somehow? (I think based on libxc changes the former,
> > but
> > it should be spelt out here I think).
> 
> Yes, it is contiguous, but I'm at a loss how to spell out the (seemingly
> obvious) fact here: "partial success, this many [less than nr_mfns]
> initial iterations done" doesn't sound much better to me. Everything
> else I can think of would require a full second sentence, which I
> wouldn't like here.

I'd perhaps write "[0, result) completed successfully" or something along
those lines.

Maybe I'm just over thinking it having the MMAP_BATCH semantics (with a
full err array) on my mind.

> > > +               requiring re-invocation by the caller with updated
> > > inputs)
> > > +   - negative (error)
> > 
> > This is a more general case of -E2BIG, you might fix that by saying
> > "other
> > error" or by moving -E2BIG to be a subclause.
> 
> "other error" would seem okay, or how about "negative (error; other
> than -E2BIG)"?

Both ok IMHO.
> 
> Jan
>

Jan Beulich Jan. 25, 2016, 2:16 p.m. UTC | #4

>>> On 25.01.16 at 15:05, <[e-mail]> wrote:
> On Mon, 2016-01-25 at 06:54 -0700, Jan Beulich wrote:
>> > > > On 25.01.16 at 13:16, <[e-mail]> wrote:
>> > On Fri, 2016-01-22 at 08:42 -0700, Jan Beulich wrote:
>> > > +#define MAP_MMIO_MAX_ITER 64 /* pretty arbitrary */
>> > > +
>> > 
>> > I suppose no existing in-tree code exceeds that (or there'd be more
>> > patch
>> > here).
>> 
>> There simply is no in-tree user other than the domctl on x86.
> 
> Right, I meant callers of the domctl (via libxc)

Then I don't understand the question. The domctl clearly can be
invoked with higher MFN counts; the #define only establishes
the cut off point for the code to return "partial success", directing
the caller to re-invoke the operation after updating inputs. I.e.
nothing else than an implementation detail which could be changed
without affecting any well behaved caller.

>> > > --- a/xen/include/public/domctl.h
>> > > +++ b/xen/include/public/domctl.h
>> > > @@ -542,8 +542,14 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_bind_
>> > >  
>> > >  
>> > >  /* Bind machine I/O address range -> HVM address range. */
>> > > -/* If this returns -E2BIG lower nr_mfns value. */
>> > >  /* XEN_DOMCTL_memory_mapping */
>> > > +/* Returns
>> > > +   - zero     (success, everything done)
>> > > +   - -E2BIG   (passed in nr_mfns value too large for the
>> > > implementation)
>> > > +   - positive (partial success, this many [less than nr_mfns] done,
>> > 
>> > Is the successful region contiguous, i.e. 0..return val, or does the
>> > caller
>> > need to figure it somehow? (I think based on libxc changes the former,
>> > but
>> > it should be spelt out here I think).
>> 
>> Yes, it is contiguous, but I'm at a loss how to spell out the (seemingly
>> obvious) fact here: "partial success, this many [less than nr_mfns]
>> initial iterations done" doesn't sound much better to me. Everything
>> else I can think of would require a full second sentence, which I
>> wouldn't like here.
> 
> I'd perhaps write "[0, result) completed successfully" or something along
> those lines.

Ah, right, that looks fine.

Thanks, Jan

Ian Campbell Jan. 25, 2016, 2:21 p.m. UTC | #5

On Mon, 2016-01-25 at 07:16 -0700, Jan Beulich wrote:
> > > > On 25.01.16 at 15:05, <[e-mail]> wrote:
> > On Mon, 2016-01-25 at 06:54 -0700, Jan Beulich wrote:
> > > > > > On 25.01.16 at 13:16, <[e-mail]> wrote:
> > > > On Fri, 2016-01-22 at 08:42 -0700, Jan Beulich wrote:
> > > > > +#define MAP_MMIO_MAX_ITER 64 /* pretty arbitrary */
> > > > > +
> > > > 
> > > > I suppose no existing in-tree code exceeds that (or there'd be more
> > > > patch
> > > > here).
> > > 
> > > There simply is no in-tree user other than the domctl on x86.
> > 
> > Right, I meant callers of the domctl (via libxc)
> 
> Then I don't understand the question. The domctl clearly can be
> invoked with higher MFN counts; the #define only establishes
> the cut off point for the code to return "partial success", directing
> the caller to re-invoke the operation after updating inputs. I.e.
> nothing else than an implementation detail which could be changed
> without affecting any well behaved caller.

Sorry, I'd confused myself into thinking the eventual caller would need to
handle the E2BIG, whereas you (of course) deal with it in the libxc
wrapper.

Ian.

Patch

--- a/tools/libxc/xc_domain.c
+++ b/tools/libxc/xc_domain.c
@@ -2174,7 +2174,7 @@  int xc_domain_memory_mapping(
 {
     DECLARE_DOMCTL;
     xc_dominfo_t info;
-    int ret = 0, err;
+    int ret = 0, rc;
     unsigned long done = 0, nr, max_batch_sz;
 
     if ( xc_domain_getinfo(xch, domid, 1, &info) != 1 ||
@@ -2199,19 +2199,24 @@  int xc_domain_memory_mapping(
         domctl.u.memory_mapping.nr_mfns = nr;
         domctl.u.memory_mapping.first_gfn = first_gfn + done;
         domctl.u.memory_mapping.first_mfn = first_mfn + done;
-        err = do_domctl(xch, &domctl);
-        if ( err && errno == E2BIG )
+        rc = do_domctl(xch, &domctl);
+        if ( rc < 0 && errno == E2BIG )
         {
             if ( max_batch_sz <= 1 )
                 break;
             max_batch_sz >>= 1;
             continue;
         }
+        if ( rc > 0 )
+        {
+            done += rc;
+            continue;
+        }
         /* Save the first error... */
         if ( !ret )
-            ret = err;
+            ret = rc;
         /* .. and ignore the rest of them when removing. */
-        if ( err && add_mapping != DPCI_REMOVE_MAPPING )
+        if ( rc && add_mapping != DPCI_REMOVE_MAPPING )
             break;
 
         done += nr;
--- a/xen/arch/x86/domain_build.c
+++ b/xen/arch/x86/domain_build.c
@@ -436,7 +436,8 @@  static __init void pvh_add_mem_mapping(s
         else
             a = p2m_access_rw;
 
-        if ( (rc = set_mmio_p2m_entry(d, gfn + i, _mfn(mfn + i), a)) )
+        if ( (rc = set_mmio_p2m_entry(d, gfn + i, _mfn(mfn + i),
+                                      PAGE_ORDER_4K, a)) )
             panic("pvh_add_mem_mapping: gfn:%lx mfn:%lx i:%ld rc:%d\n",
                   gfn, mfn, i, rc);
         if ( !(i & 0xfffff) )
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2491,7 +2491,7 @@  static int vmx_alloc_vlapic_mapping(stru
     share_xen_page_with_guest(pg, d, XENSHARE_writable);
     d->arch.hvm_domain.vmx.apic_access_mfn = mfn;
     set_mmio_p2m_entry(d, paddr_to_pfn(APIC_DEFAULT_PHYS_BASE), _mfn(mfn),
-                       p2m_get_hostp2m(d)->default_access);
+                       PAGE_ORDER_4K, p2m_get_hostp2m(d)->default_access);
 
     return 0;
 }
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -899,48 +899,62 @@  void p2m_change_type_range(struct domain
     p2m_unlock(p2m);
 }
 
-/* Returns: 0 for success, -errno for failure */
+/*
+ * Returns:
+ *    0        for success
+ *    -errno   for failure
+ *    order+1  for caller to retry with order (guaranteed smaller than
+ *             the order value passed in)
+ */
 static int set_typed_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
-                               p2m_type_t gfn_p2mt, p2m_access_t access)
+                               unsigned int order, p2m_type_t gfn_p2mt,
+                               p2m_access_t access)
 {
     int rc = 0;
     p2m_access_t a;
     p2m_type_t ot;
     mfn_t omfn;
+    unsigned int cur_order = 0;
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
 
     if ( !paging_mode_translate(d) )
         return -EIO;
 
-    gfn_lock(p2m, gfn, 0);
-    omfn = p2m->get_entry(p2m, gfn, &ot, &a, 0, NULL, NULL);
+    gfn_lock(p2m, gfn, order);
+    omfn = p2m->get_entry(p2m, gfn, &ot, &a, 0, &cur_order, NULL);
+    if ( cur_order < order )
+    {
+        gfn_unlock(p2m, gfn, order);
+        return cur_order + 1;
+    }
     if ( p2m_is_grant(ot) || p2m_is_foreign(ot) )
     {
-        gfn_unlock(p2m, gfn, 0);
+        gfn_unlock(p2m, gfn, order);
         domain_crash(d);
         return -ENOENT;
     }
     else if ( p2m_is_ram(ot) )
     {
+        unsigned long i;
+
         ASSERT(mfn_valid(omfn));
-        set_gpfn_from_mfn(mfn_x(omfn), INVALID_M2P_ENTRY);
+        for ( i = 0; i < (1UL << order); ++i )
+            set_gpfn_from_mfn(mfn_x(omfn) + i, INVALID_M2P_ENTRY);
     }
 
     P2M_DEBUG("set %d %lx %lx\n", gfn_p2mt, gfn, mfn_x(mfn));
-    rc = p2m_set_entry(p2m, gfn, mfn, PAGE_ORDER_4K, gfn_p2mt,
-                       access);
+    rc = p2m_set_entry(p2m, gfn, mfn, order, gfn_p2mt, access);
     if ( rc )
-        gdprintk(XENLOG_ERR,
-                 "p2m_set_entry failed! mfn=%08lx rc:%d\n",
-                 mfn_x(get_gfn_query_unlocked(p2m->domain, gfn, &ot)), rc);
+        gdprintk(XENLOG_ERR, "p2m_set_entry: %#lx:%u -> %d (0x%"PRI_mfn")\n",
+                 gfn, order, rc, mfn_x(mfn));
     else if ( p2m_is_pod(ot) )
     {
         pod_lock(p2m);
-        p2m->pod.entry_count--;
+        p2m->pod.entry_count -= 1UL << order;
         BUG_ON(p2m->pod.entry_count < 0);
         pod_unlock(p2m);
     }
-    gfn_unlock(p2m, gfn, 0);
+    gfn_unlock(p2m, gfn, order);
 
     return rc;
 }
@@ -949,14 +963,21 @@  static int set_typed_p2m_entry(struct do
 static int set_foreign_p2m_entry(struct domain *d, unsigned long gfn,
                                  mfn_t mfn)
 {
-    return set_typed_p2m_entry(d, gfn, mfn, p2m_map_foreign,
+    return set_typed_p2m_entry(d, gfn, mfn, PAGE_ORDER_4K, p2m_map_foreign,
                                p2m_get_hostp2m(d)->default_access);
 }
 
 int set_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
-                       p2m_access_t access)
+                       unsigned int order, p2m_access_t access)
 {
-    return set_typed_p2m_entry(d, gfn, mfn, p2m_mmio_direct, access);
+    if ( order &&
+         rangeset_overlaps_range(mmio_ro_ranges, mfn_x(mfn),
+                                 mfn_x(mfn) + (1UL << order) - 1) &&
+         !rangeset_contains_range(mmio_ro_ranges, mfn_x(mfn),
+                                  mfn_x(mfn) + (1UL << order) - 1) )
+        return order;
+
+    return set_typed_p2m_entry(d, gfn, mfn, order, p2m_mmio_direct, access);
 }
 
 int set_identity_p2m_entry(struct domain *d, unsigned long gfn,
@@ -1009,20 +1030,33 @@  int set_identity_p2m_entry(struct domain
     return ret;
 }
 
-/* Returns: 0 for success, -errno for failure */
-int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn)
+/*
+ * Returns:
+ *    0        for success
+ *    -errno   for failure
+ *    order+1  for caller to retry with order (guaranteed smaller than
+ *             the order value passed in)
+ */
+int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
+                         unsigned int order)
 {
     int rc = -EINVAL;
     mfn_t actual_mfn;
     p2m_access_t a;
     p2m_type_t t;
+    unsigned int cur_order = 0;
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
 
     if ( !paging_mode_translate(d) )
         return -EIO;
 
-    gfn_lock(p2m, gfn, 0);
-    actual_mfn = p2m->get_entry(p2m, gfn, &t, &a, 0, NULL, NULL);
+    gfn_lock(p2m, gfn, order);
+    actual_mfn = p2m->get_entry(p2m, gfn, &t, &a, 0, &cur_order, NULL);
+    if ( cur_order < order )
+    {
+        rc = cur_order + 1;
+        goto out;
+    }
 
     /* Do not use mfn_valid() here as it will usually fail for MMIO pages. */
     if ( (INVALID_MFN == mfn_x(actual_mfn)) || (t != p2m_mmio_direct) )
@@ -1035,11 +1069,11 @@  int clear_mmio_p2m_entry(struct domain *
         gdprintk(XENLOG_WARNING,
                  "no mapping between mfn %08lx and gfn %08lx\n",
                  mfn_x(mfn), gfn);
-    rc = p2m_set_entry(p2m, gfn, _mfn(INVALID_MFN), PAGE_ORDER_4K, p2m_invalid,
+    rc = p2m_set_entry(p2m, gfn, _mfn(INVALID_MFN), order, p2m_invalid,
                        p2m->default_access);
 
  out:
-    gfn_unlock(p2m, gfn, 0);
+    gfn_unlock(p2m, gfn, order);
 
     return rc;
 }
@@ -2095,6 +2129,25 @@  void *map_domain_gfn(struct p2m_domain *
     return map_domain_page(*mfn);
 }
 
+static unsigned int mmio_order(const struct domain *d,
+                               unsigned long start_fn, unsigned long nr)
+{
+    if ( !need_iommu(d) || !iommu_use_hap_pt(d) ||
+         (start_fn & ((1UL << PAGE_ORDER_2M) - 1)) || !(nr >> PAGE_ORDER_2M) )
+        return 0;
+
+    if ( !(start_fn & ((1UL << PAGE_ORDER_1G) - 1)) && (nr >> PAGE_ORDER_1G) &&
+         hap_has_1gb )
+        return PAGE_ORDER_1G;
+
+    if ( hap_has_2mb )
+        return PAGE_ORDER_2M;
+
+    return 0;
+}
+
+#define MAP_MMIO_MAX_ITER 64 /* pretty arbitrary */
+
 int map_mmio_regions(struct domain *d,
                      unsigned long start_gfn,
                      unsigned long nr,
@@ -2102,22 +2155,29 @@  int map_mmio_regions(struct domain *d,
 {
     int ret = 0;
     unsigned long i;
+    unsigned int iter, order;
 
     if ( !paging_mode_translate(d) )
         return 0;
 
-    for ( i = 0; !ret && i < nr; i++ )
+    for ( iter = i = 0; i < nr && iter < MAP_MMIO_MAX_ITER;
+          i += 1UL << order, ++iter )
     {
-        ret = set_mmio_p2m_entry(d, start_gfn + i, _mfn(mfn + i),
-                                 p2m_get_hostp2m(d)->default_access);
-        if ( ret )
+        /* OR'ing gfn and mfn values will return an order suitable to both. */
+        for ( order = mmio_order(d, (start_gfn + i) | (mfn + i), nr - i); ;
+              order = ret - 1 )
         {
-            unmap_mmio_regions(d, start_gfn, i, mfn);
-            break;
+            ret = set_mmio_p2m_entry(d, start_gfn + i, _mfn(mfn + i), order,
+                                     p2m_get_hostp2m(d)->default_access);
+            if ( ret <= 0 )
+                break;
+            ASSERT(ret <= order);
         }
+        if ( ret < 0 )
+            break;
     }
 
-    return ret;
+    return i == nr ? 0 : i ?: ret;
 }
 
 int unmap_mmio_regions(struct domain *d,
@@ -2125,20 +2185,30 @@  int unmap_mmio_regions(struct domain *d,
                        unsigned long nr,
                        unsigned long mfn)
 {
-    int err = 0;
+    int ret = 0;
     unsigned long i;
+    unsigned int iter, order;
 
     if ( !paging_mode_translate(d) )
         return 0;
 
-    for ( i = 0; i < nr; i++ )
+    for ( iter = i = 0; i < nr && iter < MAP_MMIO_MAX_ITER;
+          i += 1UL << order, ++iter )
     {
-        int ret = clear_mmio_p2m_entry(d, start_gfn + i, _mfn(mfn + i));
-        if ( ret )
-            err = ret;
+        /* OR'ing gfn and mfn values will return an order suitable to both. */
+        for ( order = mmio_order(d, (start_gfn + i) | (mfn + i), nr - i); ;
+              order = ret - 1 )
+        {
+            ret = clear_mmio_p2m_entry(d, start_gfn + i, _mfn(mfn + i), order);
+            if ( ret <= 0 )
+                break;
+            ASSERT(ret <= order);
+        }
+        if ( ret < 0 )
+            break;
     }
 
-    return err;
+    return i == nr ? 0 : i ?: ret;
 }
 
 unsigned int p2m_find_altp2m_by_eptp(struct domain *d, uint64_t eptp)
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -136,6 +136,7 @@  static void ept_p2m_type_to_flags(struct
             entry->r = entry->x = 1;
             entry->w = !rangeset_contains_singleton(mmio_ro_ranges,
                                                     entry->mfn);
+            ASSERT(entry->w || !is_epte_superpage(entry));
             entry->a = !!cpu_has_vmx_ept_ad;
             entry->d = entry->w && cpu_has_vmx_ept_ad;
             break;
--- a/xen/arch/x86/mm/p2m-pt.c
+++ b/xen/arch/x86/mm/p2m-pt.c
@@ -72,7 +72,8 @@  static const unsigned long pgt[] = {
     PGT_l3_page_table
 };
 
-static unsigned long p2m_type_to_flags(p2m_type_t t, mfn_t mfn)
+static unsigned long p2m_type_to_flags(p2m_type_t t, mfn_t mfn,
+                                       unsigned int level)
 {
     unsigned long flags;
     /*
@@ -107,6 +108,8 @@  static unsigned long p2m_type_to_flags(p
     case p2m_mmio_direct:
         if ( !rangeset_contains_singleton(mmio_ro_ranges, mfn_x(mfn)) )
             flags |= _PAGE_RW;
+        else
+            ASSERT(!level);
         return flags | P2M_BASE_FLAGS | _PAGE_PCD;
     }
 }
@@ -436,7 +439,7 @@  static int do_recalc(struct p2m_domain *
             p2m_type_t p2mt = p2m_is_logdirty_range(p2m, gfn & mask, gfn | ~mask)
                               ? p2m_ram_logdirty : p2m_ram_rw;
             unsigned long mfn = l1e_get_pfn(e);
-            unsigned long flags = p2m_type_to_flags(p2mt, _mfn(mfn));
+            unsigned long flags = p2m_type_to_flags(p2mt, _mfn(mfn), level);
 
             if ( level )
             {
@@ -573,7 +576,7 @@  p2m_pt_set_entry(struct p2m_domain *p2m,
         ASSERT(!mfn_valid(mfn) || p2mt != p2m_mmio_direct);
         l3e_content = mfn_valid(mfn) || p2m_allows_invalid_mfn(p2mt)
             ? l3e_from_pfn(mfn_x(mfn),
-                           p2m_type_to_flags(p2mt, mfn) | _PAGE_PSE)
+                           p2m_type_to_flags(p2mt, mfn, 2) | _PAGE_PSE)
             : l3e_empty();
         entry_content.l1 = l3e_content.l3;
 
@@ -609,7 +612,7 @@  p2m_pt_set_entry(struct p2m_domain *p2m,
 
         if ( mfn_valid(mfn) || p2m_allows_invalid_mfn(p2mt) )
             entry_content = p2m_l1e_from_pfn(mfn_x(mfn),
-                                             p2m_type_to_flags(p2mt, mfn));
+                                             p2m_type_to_flags(p2mt, mfn, 0));
         else
             entry_content = l1e_empty();
 
@@ -645,7 +648,7 @@  p2m_pt_set_entry(struct p2m_domain *p2m,
         ASSERT(!mfn_valid(mfn) || p2mt != p2m_mmio_direct);
         if ( mfn_valid(mfn) || p2m_allows_invalid_mfn(p2mt) )
             l2e_content = l2e_from_pfn(mfn_x(mfn),
-                                       p2m_type_to_flags(p2mt, mfn) |
+                                       p2m_type_to_flags(p2mt, mfn, 1) |
                                        _PAGE_PSE);
         else
             l2e_content = l2e_empty();
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -1046,10 +1046,12 @@  long do_domctl(XEN_GUEST_HANDLE_PARAM(xe
              (gfn + nr_mfns - 1) < gfn ) /* wrap? */
             break;
 
+#ifndef CONFIG_X86 /* XXX ARM!? */
         ret = -E2BIG;
         /* Must break hypercall up as this could take a while. */
         if ( nr_mfns > 64 )
             break;
+#endif
 
         ret = -EPERM;
         if ( !iomem_access_permitted(current->domain, mfn, mfn_end) ||
@@ -1067,7 +1069,7 @@  long do_domctl(XEN_GUEST_HANDLE_PARAM(xe
                    d->domain_id, gfn, mfn, nr_mfns);
 
             ret = map_mmio_regions(d, gfn, nr_mfns, mfn);
-            if ( ret )
+            if ( ret < 0 )
                 printk(XENLOG_G_WARNING
                        "memory_map:fail: dom%d gfn=%lx mfn=%lx nr=%lx ret:%ld\n",
                        d->domain_id, gfn, mfn, nr_mfns, ret);
@@ -1079,7 +1081,7 @@  long do_domctl(XEN_GUEST_HANDLE_PARAM(xe
                    d->domain_id, gfn, mfn, nr_mfns);
 
             ret = unmap_mmio_regions(d, gfn, nr_mfns, mfn);
-            if ( ret && is_hardware_domain(current->domain) )
+            if ( ret < 0 && is_hardware_domain(current->domain) )
                 printk(XENLOG_ERR
                        "memory_map: error %ld removing dom%d access to [%lx,%lx]\n",
                        ret, d->domain_id, mfn, mfn_end);
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -259,7 +259,7 @@  int guest_remove_page(struct domain *d,
     }
     if ( p2mt == p2m_mmio_direct )
     {
-        clear_mmio_p2m_entry(d, gmfn, _mfn(mfn));
+        clear_mmio_p2m_entry(d, gmfn, _mfn(mfn), 0);
         put_gfn(d, gmfn);
         return 1;
     }
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -574,8 +574,9 @@  int p2m_is_logdirty_range(struct p2m_dom
 
 /* Set mmio addresses in the p2m table (for pass-through) */
 int set_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
-                       p2m_access_t access);
-int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn);
+                       unsigned int order, p2m_access_t access);
+int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
+                         unsigned int order);
 
 /* Set identity addresses in the p2m table (for pass-through) */
 int set_identity_p2m_entry(struct domain *d, unsigned long gfn,
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -542,8 +542,14 @@  DEFINE_XEN_GUEST_HANDLE(xen_domctl_bind_
 
 
 /* Bind machine I/O address range -> HVM address range. */
-/* If this returns -E2BIG lower nr_mfns value. */
 /* XEN_DOMCTL_memory_mapping */
+/* Returns
+   - zero     (success, everything done)
+   - -E2BIG   (passed in nr_mfns value too large for the implementation)
+   - positive (partial success, this many [less than nr_mfns] done,
+               requiring re-invocation by the caller with updated inputs)
+   - negative (error)
+*/
 #define DPCI_ADD_MAPPING         1
 #define DPCI_REMOVE_MAPPING      0
 struct xen_domctl_memory_mapping {