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SubjectRe: [PATCH RFC 2/6] KVM: x86: extend struct kvm_vcpu_pv_apf_data with token info
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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@redhat.com>
> ---
> 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


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