RE: [RFC PATCH 4/7] x86: Add XFD faulting bit for state components

[Tian, Kevin]

> From: Zhong, Yang <yang.zhong@intel.com>
> Sent: Friday, January 7, 2022 5:32 PM
> 
> From: Jing Liu <jing2.liu@intel.com>
> 
> Intel introduces XFD faulting mechanism for extended
> XSAVE features to dynamically enable the features in
> runtime. If CPUID (EAX=0Dh, ECX=n, n>1).ECX[2] is set
> as 1, it indicates support for XFD faulting of this
> state component.
> 
> Signed-off-by: Jing Liu <jing2.liu@intel.com>
> Signed-off-by: Yang Zhong <yang.zhong@intel.com>
> ---
>  target/i386/cpu.h         | 2 +-
>  target/i386/cpu.c         | 2 +-
>  target/i386/kvm/kvm-cpu.c | 1 +
>  3 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 79023fe723..22f7ff40a6 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -1375,7 +1375,7 @@
> QEMU_BUILD_BUG_ON(sizeof(XSaveXTILE_DATA) != 0x2000);
>  typedef struct ExtSaveArea {
>      uint32_t feature, bits;
>      uint32_t offset, size;
> -    uint32_t need_align;
> +    uint32_t need_align, support_xfd;

why each flag be a 32-bit field?

also it's more natural to have them in separate lines, though I'm not
sure why existing fields are put this way (possibly due to short names?).

>  } ExtSaveArea;
> 
>  #define XSAVE_STATE_AREA_COUNT (XSTATE_XTILE_DATA_BIT + 1)
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index dd2c919c33..1adc3f0f99 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -5495,7 +5495,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t
> index, uint32_t count,
>                  const ExtSaveArea *esa = &x86_ext_save_areas[count];
>                  *eax = esa->size;
>                  *ebx = esa->offset;
> -                *ecx = esa->need_align << 1;
> +                *ecx = (esa->need_align << 1) | (esa->support_xfd << 2);
>              }
>          }
>          break;
> diff --git a/target/i386/kvm/kvm-cpu.c b/target/i386/kvm/kvm-cpu.c
> index 6c4c1c6f9d..3b3c203f11 100644
> --- a/target/i386/kvm/kvm-cpu.c
> +++ b/target/i386/kvm/kvm-cpu.c
> @@ -108,6 +108,7 @@ static void kvm_cpu_xsave_init(void)
> 
>              uint32_t ecx = kvm_arch_get_supported_cpuid(s, 0xd, i, R_ECX);
>              esa->need_align = ecx & (1u << 1) ? 1 : 0;
> +            esa->support_xfd = ecx & (1u << 2) ? 1 : 0;
>          }
>      }
>  }