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Subject[PATCH 1/2] KVM: fix cache stale memslot info with correct mmio generation number
We may cache the current mmio generation number and stale memslot info
into spte, like this scenario:

page fault: add a new memslot
read memslot and detecting its a mmio access
update memslots
update generation number
read generation number
cache the gpa and current gen number into spte

So, if guest accesses the gpa later, it will generate a incorrect
mmio exit

This patch fixes it by updating the generation number after
synchronize_srcu_expedited() that makes sure the generation
number updated only if memslots update is finished

Cc: David Matlack <>
Signed-off-by: Xiao Guangrong <>
virt/kvm/kvm_main.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 33712fb..bb40df3 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -96,7 +96,7 @@ static void hardware_disable_all(void);

static void kvm_io_bus_destroy(struct kvm_io_bus *bus);
static void update_memslots(struct kvm_memslots *slots,
- struct kvm_memory_slot *new, u64 last_generation);
+ struct kvm_memory_slot *new);

static void kvm_release_pfn_dirty(pfn_t pfn);
static void mark_page_dirty_in_slot(struct kvm *kvm,
@@ -687,8 +687,7 @@ static void sort_memslots(struct kvm_memslots *slots)

static void update_memslots(struct kvm_memslots *slots,
- struct kvm_memory_slot *new,
- u64 last_generation)
+ struct kvm_memory_slot *new)
if (new) {
int id = new->id;
@@ -699,8 +698,6 @@ static void update_memslots(struct kvm_memslots *slots,
if (new->npages != npages)
- slots->generation = last_generation + 1;

static int check_memory_region_flags(struct kvm_userspace_memory_region *mem)
@@ -722,9 +719,12 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
struct kvm_memslots *old_memslots = kvm->memslots;

- update_memslots(slots, new, kvm->memslots->generation);
+ /* ensure generation number is always increased. */
+ slots->generation = old_memslots->generation;
+ update_memslots(slots, new);
rcu_assign_pointer(kvm->memslots, slots);
+ slots->generation++;


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