Siddharth Chandrasekaran <sidcha@xxxxxxxxx> writes: > On Thu, Apr 08, 2021 at 02:05:53PM +0200, Vitaly Kuznetsov wrote: >> Siddharth Chandrasekaran <sidcha@xxxxxxxxx> 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@xxxxxxxxxx> >> > Cc: Evgeny Iakovlev <eyakovl@xxxxxxxxx> >> > Signed-off-by: Siddharth Chandrasekaran <sidcha@xxxxxxxxx> >> > --- >> > 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). > > That is how I had it initially; but then noticed that we would never > need to use either of them separately. So it seemed like a reasonable > abstraction to put them together. > Actually, we may. In theory, KVM userspace may decide to expose just one of these two to the guest as it is not obliged to copy everything from KVM_GET_SUPPORTED_HV_CPUID so we will need separate guest_cpuid_has() checks. (This reminds me of something I didn't see in your series: we need to check that XMM hypercall parameters support was actually exposed to the guest as it is illegal for a guest to use it otherwise -- and we will likely need two checks, for input and output). Also, (and that's what triggered my comment) all other HV_ACCESS_* in kvm_get_hv_cpuid() are single bits so my first impression was that you forgot one bit, but then I saw that you combined them together. -- Vitaly
