Re: [PATCH v3 02/12] KVM: x86/mmu: bump mmu notifier count in kvm_zap_gfn_range

[Paolo Bonzini <pbonzini@redhat.com>]

On 02/08/21 20:33, Maxim Levitsky wrote:
> 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 9d78cb1c0f35..9da635e383c2 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5640,6 +5640,8 @@ 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);
> @@ -5671,6 +5673,8 @@ 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 9d6b4ad407b8..962e11a73e8e 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -985,6 +985,11 @@ 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 a96cbe24c688..71042cd807b3 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -608,7 +608,7 @@ 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)
>   {
>   	/*
> @@ -636,6 +636,7 @@ 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)
> @@ -670,7 +671,7 @@ 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)
>   {
>   	/*
> @@ -687,6 +688,8 @@ 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)
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>