From: Sean Christopherson <seanjc@xxxxxxxxxx>
[ Upstream commit e0c378684b6545ad2d4403bb701d0ac4932b4e95 ]
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: 2f2fad0897cb ("kvm: x86/mmu: Add functions to handle changed TDP SPTEs")
Cc: Ben Gardon <bgardon@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-Id: <20210225204749.1512652-6-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 2d37068b7cd5..2f2576fd343e 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3663,6 +3663,14 @@ 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;
--
2.30.2
