KVM: x86/mmu: Detect MMIO generation wrap in any address space

The check to detect a wrap of the MMIO generation explicitly looks for a
generation number of zero.  Now that unique memslots generation numbers
are assigned to each address space, only address space 0 will get a
generation number of exactly zero when wrapping.  E.g. when address
space 1 goes from 0x7fffe to 0x80002, the MMIO generation number will
wrap to 0x2.  Adjust the MMIO generation to strip the address space
modifier prior to checking for a wrap.

Fixes: 4bd518f1598d ("KVM: use separate generations for each address space")
Cc: <stable@vger.kernel.org>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 19 insertions, 2 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index a53a0e7ad9e63..c2f2c9de63ed9 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -5895,11 +5895,28 @@ static bool kvm_has_zapped_obsolete_pages(struct kvm *kvm)
 
 void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen)
 {
+	gen &= MMIO_GEN_MASK;
+
+	/*
+	 * Shift to eliminate the "update in-progress" flag, which isn't
+	 * included in the spte's generation number.
+	 */
+	gen >>= 1;
+
+	/*
+	 * Generation numbers are incremented in multiples of the number of
+	 * address spaces in order to provide unique generations across all
+	 * address spaces.  Strip what is effectively the address space
+	 * modifier prior to checking for a wrap of the MMIO generation so
+	 * that a wrap in any address space is detected.
+	 */
+	gen &= ~((u64)KVM_ADDRESS_SPACE_NUM - 1);
+
 	/*
-	 * The very rare case: if the generation-number is round,
+	 * The very rare case: if the MMIO generation number has wrapped,
 	 * zap all shadow pages.
 	 */
-	if (unlikely((gen & MMIO_GEN_MASK) == 0)) {
+	if (unlikely(gen == 0)) {
 		kvm_debug_ratelimited("kvm: zapping shadow pages for mmio generation wraparound\n");
 		kvm_mmu_invalidate_zap_all_pages(kvm);
 	}