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KVM: x86/mmu: Check for !leaf=>leaf, not PFN change, in TDP MMU SP removal

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Look for a !leaf=>leaf conversion instead of a PFN change when checking
if a SPTE change removed a TDP MMU shadow page.  Convert the PFN check
into a WARN, as KVM should never change the PFN of a shadow page (except
when its being zapped or replaced).

From a purely theoretical perspective, it's not illegal to replace a SP
with a hugepage pointing at the same PFN.  In practice, it's impossible
as that would require mapping guest memory overtop a kernel-allocated SP.
Either way, the check is odd.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Message-Id: <20220226001546.360188-8-seanjc@google.com>
Reviewed-by: Mingwei Zhang <mizhang@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2022-02-26 00:15:25 +00:00 committed by Paolo Bonzini
parent 614f6970aa
commit c8e5a0d0e9
1 changed files with 5 additions and 2 deletions
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7
arch/x86/kvm/mmu/tdp_mmu.c
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@ -491,9 +491,12 @@ static void __handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
/*
* Recursively handle child PTs if the change removed a subtree from
* the paging structure.
* the paging structure. Note the WARN on the PFN changing without the
* SPTE being converted to a hugepage (leaf) or being zapped. Shadow
* pages are kernel allocations and should never be migrated.
*/
if (was_present && !was_leaf && (pfn_changed || !is_present))
if (was_present && !was_leaf &&
(is_leaf || !is_present || WARN_ON_ONCE(pfn_changed)))
handle_removed_pt(kvm, spte_to_child_pt(old_spte, level), shared);
}