[5/5] IOMMU: iommu_snoop is x86/HVM-only

Commit Message

Jan Beulich Feb. 28, 2020, 12:27 p.m. UTC

In fact it's VT-d specific, but we don't have a way yet to build code
for just one vendor. Provide a #define for all other cases.

Signed-off-by: Jan Beulich <[e-mail]>

Comments

Andrew Cooper Feb. 28, 2020, 8:20 p.m. UTC | #1

On 28/02/2020 12:27, Jan Beulich wrote:
> In fact it's VT-d specific, but we don't have a way yet to build code
> for just one vendor. Provide a #define for all other cases.
>
> Signed-off-by: Jan Beulich <[e-mail]>

iommu_snoop has no specific interaction with HVM.

It is for any cacheability games the hypervisor may play on a VM, and
that in principle includes PV guests as well.

~Andrew

Jan Beulich March 2, 2020, 10:14 a.m. UTC | #2

On 28.02.2020 21:20, Andrew Cooper wrote:
> On 28/02/2020 12:27, Jan Beulich wrote:
>> In fact it's VT-d specific, but we don't have a way yet to build code
>> for just one vendor. Provide a #define for all other cases.
>>
>> Signed-off-by: Jan Beulich <[e-mail]>
> 
> iommu_snoop has no specific interaction with HVM.
> 
> It is for any cacheability games the hypervisor may play on a VM, and
> that in principle includes PV guests as well.

Oh, in the grep results I overlooked

    /* Set the SNP on leaf page table if Snoop Control available */
    if ( iommu_snoop )
        dma_set_pte_snp(new);

Thanks for pointing out, will correct.

Jan

Patch

--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -32,7 +32,6 @@  bool_t __read_mostly iommu_enabled;
 bool_t __read_mostly force_iommu;
 bool_t __read_mostly iommu_verbose;
 bool __read_mostly iommu_quarantine = true;
-bool_t __read_mostly iommu_snoop = 1;
 bool_t __read_mostly iommu_crash_disable;
 
 static bool __hwdom_initdata iommu_hwdom_none;
@@ -79,8 +78,10 @@  static int __init parse_iommu_param(cons
 #endif
         else if ( (val = parse_boolean("verbose", s, ss)) >= 0 )
             iommu_verbose = val;
+#ifndef iommu_snoop
         else if ( (val = parse_boolean("snoop", s, ss)) >= 0 )
             iommu_snoop = val;
+#endif
 #ifndef iommu_intremap
         else if ( (val = parse_boolean("intremap", s, ss)) >= 0 )
             iommu_intremap = val ? iommu_intremap_full : iommu_intremap_off;
@@ -488,7 +489,9 @@  int __init iommu_setup(void)
     printk("I/O virtualisation %sabled\n", iommu_enabled ? "en" : "dis");
     if ( !iommu_enabled )
     {
-        iommu_snoop = 0;
+#ifndef iommu_snoop
+        iommu_snoop = false;
+#endif
         iommu_hwdom_passthrough = false;
         iommu_hwdom_strict = false;
     }
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -52,6 +52,9 @@  bool __read_mostly untrusted_msi;
 
 bool __read_mostly iommu_igfx = true;
 bool __read_mostly iommu_qinval = true;
+#ifndef iommu_snoop
+bool __read_mostly iommu_snoop = true;
+#endif
 
 int nr_iommus;
 
@@ -2288,8 +2291,10 @@  static int __init vtd_setup(void)
                cap_sps_2mb(iommu->cap) ? ", 2MB" : "",
                cap_sps_1gb(iommu->cap) ? ", 1GB" : "");
 
+#ifndef iommu_snoop
         if ( iommu_snoop && !ecap_snp_ctl(iommu->ecap) )
-            iommu_snoop = 0;
+            iommu_snoop = false;
+#endif
 
         if ( iommu_hwdom_passthrough && !ecap_pass_thru(iommu->ecap) )
             iommu_hwdom_passthrough = false;
@@ -2331,7 +2336,9 @@  static int __init vtd_setup(void)
     }
 
 #define P(p,s) printk("Intel VT-d %s %senabled.\n", s, (p)? "" : "not ")
+#ifndef iommu_snoop
     P(iommu_snoop, "Snoop Control");
+#endif
     P(iommu_hwdom_passthrough, "Dom0 DMA Passthrough");
     P(iommu_qinval, "Queued Invalidation");
     P(iommu_intremap, "Interrupt Remapping");
@@ -2351,7 +2358,9 @@  static int __init vtd_setup(void)
 
  error:
     iommu_enabled = 0;
-    iommu_snoop = 0;
+#ifndef iommu_snoop
+    iommu_snoop = false;
+#endif
     iommu_hwdom_passthrough = false;
     iommu_qinval = 0;
     iommu_intremap = iommu_intremap_off;
--- a/xen/include/xen/iommu.h
+++ b/xen/include/xen/iommu.h
@@ -54,7 +54,6 @@  static inline bool_t dfn_eq(dfn_t x, dfn
 
 extern bool_t iommu_enable, iommu_enabled;
 extern bool force_iommu, iommu_quarantine, iommu_verbose;
-extern bool_t iommu_snoop;
 
 #ifdef CONFIG_X86
 extern enum __packed iommu_intremap {
@@ -72,9 +71,10 @@  extern bool iommu_igfx, iommu_qinval;
 #endif
 
 #if defined(CONFIG_X86) && defined(CONFIG_HVM)
-extern bool iommu_intpost;
+extern bool iommu_intpost, iommu_snoop;
 #else
 # define iommu_intpost false
+# define iommu_snoop false
 #endif
 
 #if defined(CONFIG_IOMMU_FORCE_PT_SHARE)