Commit c8e5a0d0 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

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



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: default avatarSean Christopherson <seanjc@google.com>
Reviewed-by: default avatarBen Gardon <bgardon@google.com>
Message-Id: <20220226001546.360188-8-seanjc@google.com>
Reviewed-by: default avatarMingwei Zhang <mizhang@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 614f6970

arch/x86/kvm/mmu/tdp_mmu.c

+5 −2
Original line number Diff line number Diff line
@@ -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);

}