KVM: Move the memslot update in-progress flag to bit 63

...now that KVM won't explode by moving it out of bit 0.  Using bit 63
eliminates the need to jump over bit 0, e.g. when calculating a new
memslots generation or when propagating the memslots generation to an
MMIO spte.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 12 insertions, 19 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 364b2a737d94c..bcf62e1e1ff79 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -335,18 +335,17 @@ static inline bool is_access_track_spte(u64 spte)
  * Due to limited space in PTEs, the MMIO generation is a 19 bit subset of
  * the memslots generation and is derived as follows:
  *
- * Bits 1-9 of the memslot generation are propagated to spte bits 3-11
- * Bits 10-19 of the memslot generation are propagated to spte bits 52-61
+ * Bits 0-8 of the MMIO generation are propagated to spte bits 3-11
+ * Bits 9-18 of the MMIO generation are propagated to spte bits 52-61
  *
- * The MMIO generation starts at bit 1 of the memslots generation in order to
- * skip over bit 0, the KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS flag.  Including
- * the flag would require stealing a bit from the "real" generation number and
- * thus effectively halve the maximum number of MMIO generations that can be
- * handled before encountering a wrap (which requires a full MMU zap).  The
- * flag is instead explicitly queried when checking for MMIO spte cache hits.
+ * The KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS flag is intentionally not included in
+ * the MMIO generation number, as doing so would require stealing a bit from
+ * the "real" generation number and thus effectively halve the maximum number
+ * of MMIO generations that can be handled before encountering a wrap (which
+ * requires a full MMU zap).  The flag is instead explicitly queried when
+ * checking for MMIO spte cache hits.
  */
-#define MMIO_SPTE_GEN_MASK		GENMASK_ULL(19, 1)
-#define MMIO_SPTE_GEN_SHIFT		1
+#define MMIO_SPTE_GEN_MASK		GENMASK_ULL(18, 0)
 
 #define MMIO_SPTE_GEN_LOW_START		3
 #define MMIO_SPTE_GEN_LOW_END		11
@@ -363,8 +362,6 @@ static u64 generation_mmio_spte_mask(u64 gen)
 
 	WARN_ON(gen & ~MMIO_SPTE_GEN_MASK);
 
-	gen >>= MMIO_SPTE_GEN_SHIFT;
-
 	mask = (gen << MMIO_SPTE_GEN_LOW_START) & MMIO_SPTE_GEN_LOW_MASK;
 	mask |= (gen << MMIO_SPTE_GEN_HIGH_START) & MMIO_SPTE_GEN_HIGH_MASK;
 	return mask;
@@ -378,7 +375,7 @@ static u64 get_mmio_spte_generation(u64 spte)
 
 	gen = (spte & MMIO_SPTE_GEN_LOW_MASK) >> MMIO_SPTE_GEN_LOW_START;
 	gen |= (spte & MMIO_SPTE_GEN_HIGH_MASK) >> MMIO_SPTE_GEN_HIGH_START;
-	return gen << MMIO_SPTE_GEN_SHIFT;
+	return gen;
 }
 
 static void mark_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, u64 gfn,
@@ -5905,13 +5902,9 @@ static bool kvm_has_zapped_obsolete_pages(struct kvm *kvm)
 
 void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen)
 {
-	gen &= MMIO_SPTE_GEN_MASK;
+	WARN_ON(gen & KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS);
 
-	/*
-	 * Shift to adjust for the "update in-progress" flag, which isn't
-	 * included in the MMIO generation number.
-	 */
-	gen >>= MMIO_SPTE_GEN_SHIFT;
+	gen &= MMIO_SPTE_GEN_MASK;
 
 	/*
 	 * Generation numbers are incremented in multiples of the number of