Commit e0c37868 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86/mmu: Retry page faults that hit an invalid memslot 



Retry page faults (re-enter the guest) that hit an invalid memslot
instead of treating the memslot as not existing, i.e. handling the
page fault as an MMIO access.  When deleting a memslot, SPTEs aren't
zapped and the TLBs aren't flushed until after the memslot has been
marked invalid.

Handling the invalid slot as MMIO means there's a small window where a
page fault could replace a valid SPTE with an MMIO SPTE.  The legacy
MMU handles such a scenario cleanly, but the TDP MMU assumes such
behavior is impossible (see the BUG() in __handle_changed_spte()).
There's really no good reason why the legacy MMU should allow such a
scenario, and closing this hole allows for additional cleanups.

Fixes: 2f2fad08 ("kvm: x86/mmu: Add functions to handle changed TDP SPTEs")
Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-6-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 44aaa015

arch/x86/kvm/mmu/mmu.c

+8 −0
Original line number Diff line number Diff line
@@ -3683,6 +3683,14 @@ static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn, 
	struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);

	bool async;



	/*

	 * Retry the page fault if the gfn hit a memslot that is being deleted

	 * or moved.  This ensures any existing SPTEs for the old memslot will

	 * be zapped before KVM inserts a new MMIO SPTE for the gfn.

	 */

	if (slot && (slot->flags & KVM_MEMSLOT_INVALID))

		return true;



	/* Don't expose private memslots to L2. */

	if (is_guest_mode(vcpu) && !kvm_is_visible_memslot(slot)) {

		*pfn = KVM_PFN_NOSLOT;