Re: [PATCH 4/4] KVM: hyper-v: Advertise support for fast XMM hypercalls

Vitaly Kuznetsov
2021-04-08T12:06:03Z

Siddharth Chandrasekaran <sidcha@amazon.de> writes:

> Now that all extant hypercalls that can use XMM registers (based on
> spec) for input/outputs are patched to support them, we can start
> advertising this feature to guests.
>
> Cc: Alexander Graf <graf@amazon.com>
> Cc: Evgeny Iakovlev <eyakovl@amazon.de>
> Signed-off-by: Siddharth Chandrasekaran <sidcha@amazon.de>
> ---
> arch/x86/include/asm/hyperv-tlfs.h | 4 ++--
> arch/x86/kvm/hyperv.c | 1 +
> 2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> index e6cd3fee562b..1f160ef60509 100644
> --- a/arch/x86/include/asm/hyperv-tlfs.h
> +++ b/arch/x86/include/asm/hyperv-tlfs.h
> @@ -49,10 +49,10 @@
> /* Support for physical CPU dynamic partitioning events is available*/
> #define HV_X64_CPU_DYNAMIC_PARTITIONING_AVAILABLE BIT(3)
> /*
> - * Support for passing hypercall input parameter block via XMM
> + * Support for passing hypercall input and output parameter block via XMM
> * registers is available
> */
> -#define HV_X64_HYPERCALL_PARAMS_XMM_AVAILABLE BIT(4)
> +#define HV_X64_HYPERCALL_PARAMS_XMM_AVAILABLE BIT(4) | BIT(15)

TLFS 6.0b states that there are two distinct bits for input and output:

CPUID Leaf 0x40000003.EDX:
Bit 4: support for passing hypercall input via XMM registers is available.
Bit 15: support for returning hypercall output via XMM registers is available.

and HV_X64_HYPERCALL_PARAMS_XMM_AVAILABLE is not currently used
anywhere, I'd suggest we just rename

HV_X64_HYPERCALL_PARAMS_XMM_AVAILABLE to HV_X64_HYPERCALL_XMM_INPUT_AVAILABLE
and add HV_X64_HYPERCALL_XMM_OUTPUT_AVAILABLE (bit 15).

> /* Support for a virtual guest idle state is available */
> #define HV_X64_GUEST_IDLE_STATE_AVAILABLE BIT(5)
> /* Frequency MSRs available */
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index bf2f86f263f1..dd462c1d641d 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -2254,6 +2254,7 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
> ent->ebx |= HV_POST_MESSAGES;
> ent->ebx |= HV_SIGNAL_EVENTS;
>
> + ent->edx |= HV_X64_HYPERCALL_PARAMS_XMM_AVAILABLE;
> ent->edx |= HV_FEATURE_FREQUENCY_MSRS_AVAILABLE;
> ent->edx |= HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE;

--
Vitaly