From: Sean Christopherson seanjc@google.com
[ 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@google.com Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20210225204749.1512652-6-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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;