[2/3] x86/P2M: correct old entry checking in p2m_remove_entry()

Commit Message

Jan Beulich Feb. 26, 2025, 11:52 a.m. UTC

Using p2m_is_valid() isn't quite right here. It expanding to RAM+MMIO,
the subsequent p2m_mmio_direct check effectively reduces its use to
RAM+MMIO_DM. Yet MMIO_DM entries, which are never marked present in the
page tables, won't pass the mfn_valid() check. It is, however, quite
plausible (and supported by the rest of the function) to permit
"removing" hole entries, i.e. in particular to convert MMIO_DM to
INVALID. Which leaves the original check to be against RAM (plus MFN
validity), while HOLE then instead wants INVALID_MFN to be passed in.

Further more grant and foreign entries (together with RAM becoming
ANY_RAM) as well as BROKEN want the MFN checking, too.

All other types (i.e. MMIO_DIRECT and POD) want rejecting here rather
than skipping, for needing handling / accounting elsewhere.

Signed-off-by: Jan Beulich <[e-mail]>
---
Paging/sharing types likely need further customization here. Paths
leading here differ in their handling (e.g. guest_remove_page() special-
casing paging types vs XENMEM_remove_from_physmap not doing so), so it's
not even clear what the intentions are for those types.

Patch

--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -531,9 +531,9 @@  p2m_remove_entry(struct p2m_domain *p2m,
         mfn_t mfn_return = p2m->get_entry(p2m, gfn_add(gfn, i), &t, &a, 0,
                                           &cur_order, NULL);
 
-        if ( p2m_is_valid(t) &&
-             (!mfn_valid(mfn) || t == p2m_mmio_direct ||
-              !mfn_eq(mfn_add(mfn, i), mfn_return)) )
+        if ( p2m_is_any_ram(t) || p2m_is_broken(t)
+             ? !mfn_valid(mfn) || !mfn_eq(mfn_add(mfn, i), mfn_return)
+             : !p2m_is_hole(t) || !mfn_eq(mfn, INVALID_MFN) )
             return -EILSEQ;
 
         i += (1UL << cur_order) -