[PATCH v4 04/16] KVM: x86/mmu: bump mmu notifier count in kvm_zap_gfn_range

Maxim Levitsky
2021-08-10T20:53:30Z

This together with previous patch, ensures that
kvm_zap_gfn_range doesn't race with page fault
running on another vcpu, and will make this page fault code
retry instead.

This is based on a patch suggested by Sean Christopherson:
https://lkml.org/lkml/2021/7/22/1025

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/kvm/mmu/mmu.c | 4 ++++
include/linux/kvm_host.h | 5 +++++
virt/kvm/kvm_main.c | 7 +++++--
3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index d4e22a9635a9..abaf8e661c61 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5660,6 +5660,8 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)

write_lock(&kvm->mmu_lock);

+ kvm_inc_notifier_count(kvm, gfn_start, gfn_end);
+
if (kvm_memslots_have_rmaps(kvm)) {
for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
slots = __kvm_memslots(kvm, i);
@@ -5695,6 +5697,8 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
if (flush)
kvm_flush_remote_tlbs_with_address(kvm, gfn_start, gfn_end);

+ kvm_dec_notifier_count(kvm, gfn_start, gfn_end);
+
write_unlock(&kvm->mmu_lock);
}

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f50bfcf225f0..4e43843fe0d7 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -991,6 +991,11 @@ void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc);
void *kvm_mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
#endif

+void kvm_inc_notifier_count(struct kvm *kvm, unsigned long start,
+ unsigned long end);
+void kvm_dec_notifier_count(struct kvm *kvm, unsigned long start,
+ unsigned long end);
+
long kvm_arch_dev_ioctl(struct file *filp,
unsigned int ioctl, unsigned long arg);
long kvm_arch_vcpu_ioctl(struct file *filp,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a438a7a3774a..46f55e860b8b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -610,7 +610,7 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
}

-static void kvm_inc_notifier_count(struct kvm *kvm, unsigned long start,
+void kvm_inc_notifier_count(struct kvm *kvm, unsigned long start,
unsigned long end)
{
/*
@@ -638,6 +638,7 @@ static void kvm_inc_notifier_count(struct kvm *kvm, unsigned long start,
max(kvm->mmu_notifier_range_end, end);
}
}
+EXPORT_SYMBOL_GPL(kvm_inc_notifier_count);

static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
const struct mmu_notifier_range *range)
@@ -672,7 +673,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
return 0;
}

-static void kvm_dec_notifier_count(struct kvm *kvm, unsigned long start,
+void kvm_dec_notifier_count(struct kvm *kvm, unsigned long start,
unsigned long end)
{
/*
@@ -689,6 +690,8 @@ static void kvm_dec_notifier_count(struct kvm *kvm, unsigned long start,
*/
kvm->mmu_notifier_count--;
}
+EXPORT_SYMBOL_GPL(kvm_dec_notifier_count);
+

static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
const struct mmu_notifier_range *range)
--
2.26.3