KVM: x86/mmu: Shove refcounted page dependency into host_pfn_mapping_level()

Move the check that restricts mapping huge pages into the guest to pfns
that are backed by refcounted 'struct page' memory into the helper that
actually "requires" a 'struct page', host_pfn_mapping_level().  In
addition to deduplicating code, moving the check to the helper eliminates
the subtle requirement that the caller check that the incoming pfn is
backed by a refcounted struct page, and as an added bonus avoids an extra
pfn_to_page() lookup.

Note, the is_error_noslot_pfn() check in kvm_mmu_hugepage_adjust() needs
to stay where it is, as it guards against dereferencing a NULL memslot in
the kvm_slot_dirty_track_enabled() that follows.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220429010416.2788472-11-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 7ebb97c..27b2a56 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2791,8 +2791,8 @@ static void direct_pte_prefetch(struct kvm_vcpu *vcpu, u64 *sptep)
 static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
                                  const struct kvm_memory_slot *slot)
 {
-       struct page *page = pfn_to_page(pfn);
        int level = PG_LEVEL_4K;
+       struct page *page;
        unsigned long hva;
        unsigned long flags;
        pgd_t pgd;
@@ -2800,6 +2800,14 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
        pud_t pud;
        pmd_t pmd;
 
+       /*
+        * Note, @slot must be non-NULL, i.e. the caller is responsible for
+        * ensuring @pfn isn't garbage and is backed by a memslot.
+        */
+       page = kvm_pfn_to_refcounted_page(pfn);
+       if (!page)
+               return PG_LEVEL_4K;
+
        if (!PageCompound(page) && !kvm_is_zone_device_page(page))
                return PG_LEVEL_4K;
 
@@ -2884,7 +2892,7 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
        if (unlikely(fault->max_level == PG_LEVEL_4K))
                return;
 
-       if (is_error_noslot_pfn(fault->pfn) || !kvm_pfn_to_refcounted_page(fault->pfn))
+       if (is_error_noslot_pfn(fault->pfn))
                return;
 
        if (kvm_slot_dirty_track_enabled(slot))
@@ -5996,7 +6004,7 @@ restart:
                 * the guest, and the guest page table is using 4K page size
                 * mapping if the indirect sp has level = 1.
                 */
-               if (sp->role.direct && kvm_pfn_to_refcounted_page(pfn) &&
+               if (sp->role.direct &&
                    sp->role.level < kvm_mmu_max_mapping_level(kvm, slot, sp->gfn,
                                                               pfn, PG_LEVEL_NUM)) {
                        pte_list_remove(kvm, rmap_head, sptep);

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 1e777b7..1ea4080 100644 (file)
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1750,10 +1750,6 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
                 * be mapped at a higher level.
                 */
                pfn = spte_to_pfn(iter.old_spte);
-
-               if (!kvm_pfn_to_refcounted_page(pfn))
-                       continue;
-
                max_mapping_level = kvm_mmu_max_mapping_level(kvm, slot,
                                iter.gfn, pfn, PG_LEVEL_NUM);