Re: [PATCH v2 10/10] KVM: x86/mmu: check for invalid async page faults involving private memory

[Xiaoyao Li <xiaoyao.li@xxxxxxxxx>]

On 4/17/2024 4:19 AM, Paolo Bonzini wrote:
> Right now the error code is not used when an async page fault is completed.
> This is not a problem in the current code, but it is untidy.  For protected
> VMs, we will also need to check that the page attributes match the current
> state of the page, because asynchronous page faults can only occur on
> shared pages (private pages go through kvm_faultin_pfn_private() instead of
> __gfn_to_pfn_memslot()).
>
> Start by piping the error code from kvm_arch_setup_async_pf() to
> kvm_arch_async_page_ready() via the architecture-specific async page
> fault data.  

It is missed in this patch ...

> For now, it can be used to assert that there are no
> async page faults on private memory.
>
> Extracted from a patch by Isaku Yamahata.
>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
>   arch/x86/include/asm/kvm_host.h |  1 +
>   arch/x86/kvm/mmu/mmu.c          | 17 ++++++++++-------
>   2 files changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 7c73952b6f4e..57ec96bd4221 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1850,6 +1850,7 @@ struct kvm_arch_async_pf {
>   	gfn_t gfn;
>   	unsigned long cr3;
>   	bool direct_map;
> +	u64 error_code;
>   };
>   
>   extern u32 __read_mostly kvm_nr_uret_msrs;
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 33aea47dce8b..402d04aa5423 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4207,24 +4207,27 @@ static u32 alloc_apf_token(struct kvm_vcpu *vcpu)
>   	return (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id;
>   }
>   
> -static bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> -				    gfn_t gfn)
> +static bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu,
> +				    struct kvm_page_fault *fault)
>   {
>   	struct kvm_arch_async_pf arch;
>   
>   	arch.token = alloc_apf_token(vcpu);
> -	arch.gfn = gfn;
> +	arch.gfn = fault->gfn;
>   	arch.direct_map = vcpu->arch.mmu->root_role.direct;
>   	arch.cr3 = kvm_mmu_get_guest_pgd(vcpu, vcpu->arch.mmu);

+ 	arch.error_code = fault->error_code;

>   
> -	return kvm_setup_async_pf(vcpu, cr2_or_gpa,
> -				  kvm_vcpu_gfn_to_hva(vcpu, gfn), &arch);
> +	return kvm_setup_async_pf(vcpu, fault->addr,
> +				  kvm_vcpu_gfn_to_hva(vcpu, fault->gfn), &arch);
>   }
>   
>   void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
>   {
>   	int r;
>   
> +	if (WARN_ON_ONCE(work->arch.error_code & PFERR_GUEST_ENC_MASK))
> +		return;
> +
>   	if ((vcpu->arch.mmu->root_role.direct != work->arch.direct_map) ||
>   	      work->wakeup_all)
>   		return;
> @@ -4237,7 +4240,7 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
>   	      work->arch.cr3 != kvm_mmu_get_guest_pgd(vcpu, vcpu->arch.mmu))
>   		return;
>   
> -	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true, NULL);
> +	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, work->arch.error_code, true, NULL);
>   }
>   
>   static inline u8 kvm_max_level_for_order(int order)
> @@ -4342,7 +4345,7 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
>   			trace_kvm_async_pf_repeated_fault(fault->addr, fault->gfn);
>   			kvm_make_request(KVM_REQ_APF_HALT, vcpu);
>   			return RET_PF_RETRY;
> -		} else if (kvm_arch_setup_async_pf(vcpu, fault->addr, fault->gfn)) {
> +		} else if (kvm_arch_setup_async_pf(vcpu, fault)) {
>   			return RET_PF_RETRY;
>   		}
>   	}