Re: [PATCH RFC 2/6] KVM: x86: extend struct kvm_vcpu_pv_apf_data with token info

[Gavin Shan <gshan@xxxxxxxxxx>]

Hi Vitaly,

On 4/29/20 7:36 PM, Vitaly Kuznetsov wrote:
> Currently, APF mechanism relies on the #PF abuse where the token is being
> passed through CR2. If we switch to using interrupts to deliver page-ready
> notifications we need a different way to pass the data. Extent the existing
> 'struct kvm_vcpu_pv_apf_data' with token information.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
>   arch/x86/include/uapi/asm/kvm_para.h |  3 ++-
>   arch/x86/kvm/x86.c                   | 10 ++++++----
>   2 files changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
> index 2a8e0b6b9805..df2ba34037a2 100644
> --- a/arch/x86/include/uapi/asm/kvm_para.h
> +++ b/arch/x86/include/uapi/asm/kvm_para.h
> @@ -113,7 +113,8 @@ struct kvm_mmu_op_release_pt {
>   
>   struct kvm_vcpu_pv_apf_data {
>   	__u32 reason;
> -	__u8 pad[60];
> +	__u32 token;
> +	__u8 pad[56];
>   	__u32 enabled;
>   };
>   
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b93133ee07ba..7c21c0cf0a33 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2662,7 +2662,7 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
>   	}
>   
>   	if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa,
> -					sizeof(u32)))
> +					sizeof(u64)))
>   		return 1;
>   
>   	vcpu->arch.apf.send_user_only = !(data & KVM_ASYNC_PF_SEND_ALWAYS);
> @@ -10352,8 +10352,9 @@ static void kvm_del_async_pf_gfn(struct kvm_vcpu *vcpu, gfn_t gfn)
>   	}
>   }
>   
> -static int apf_put_user(struct kvm_vcpu *vcpu, u32 val)
> +static int apf_put_user(struct kvm_vcpu *vcpu, u32 reason, u32 token)
>   {
> +	u64 val = (u64)token << 32 | reason;
>   
>   	return kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.apf.data, &val,
>   				      sizeof(val));
> @@ -10405,7 +10406,8 @@ void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
>   	kvm_add_async_pf_gfn(vcpu, work->arch.gfn);
>   
>   	if (kvm_can_deliver_async_pf(vcpu) &&
> -	    !apf_put_user(vcpu, KVM_PV_REASON_PAGE_NOT_PRESENT)) {
> +	    !apf_put_user(vcpu, KVM_PV_REASON_PAGE_NOT_PRESENT,
> +			  work->arch.token)) {
>   		fault.vector = PF_VECTOR;
>   		fault.error_code_valid = true;
>   		fault.error_code = 0;
> @@ -10438,7 +10440,7 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
>   	trace_kvm_async_pf_ready(work->arch.token, work->cr2_or_gpa);
>   
>   	if (vcpu->arch.apf.msr_val & KVM_ASYNC_PF_ENABLED &&
> -	    !apf_put_user(vcpu, KVM_PV_REASON_PAGE_READY)) {
> +	    !apf_put_user(vcpu, KVM_PV_REASON_PAGE_READY, work->arch.token)) {
>   			fault.vector = PF_VECTOR;
>   			fault.error_code_valid = true;
>   			fault.error_code = 0;

It would be as below based on two facts: (1) token is more important than reason;
(2) token will be put into high word of @val. I think apf_{get,put}_user() might
be worthy to be inline. However, it's not a big deal.

   static inline int apf_put_user(struct kvm_vcpu *vcpu, u32 token, u32 reason)

Thanks,
Gavin