RE: [RFC PATCH 1/7] x86: Fix the 64-byte boundary enumeration for extended state

[Tian, Kevin]

> From: Zhong, Yang <yang.zhong@intel.com>
> Sent: Friday, January 7, 2022 5:31 PM
> 
> From: Jing Liu <jing2.liu@intel.com>
> 
> The extended state subleaves (EAX=0Dh, ECX=n, n>1).ECX[1]
> are all zero, while spec actually introduces that bit 01
> should indicate if the extended state component locates
> on the next 64-byte boundary following the preceding state
> component when the compacted format of an XSAVE area is
> used.

Above would read clearer if you revise to:

"The extended state subleaves (EAX=0Dh, ECX=n, n>1).ECX[1]
indicate whether the extended state component locates
on the next 64-byte boundary following the preceding state
component when the compacted format of an XSAVE area is
used.

But ECX[1] is always cleared in current implementation."

> 
> Fix the subleaves value according to the host supported
> cpuid. The upcoming AMX feature would be the first one
> using it.
> 
> Signed-off-by: Jing Liu <jing2.liu@intel.com>
> Signed-off-by: Yang Zhong <yang.zhong@intel.com>
> ---
>  target/i386/cpu.h         | 1 +
>  target/i386/cpu.c         | 1 +
>  target/i386/kvm/kvm-cpu.c | 3 +++
>  3 files changed, 5 insertions(+)
> 
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 04f2b790c9..7f9700544f 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -1354,6 +1354,7 @@ QEMU_BUILD_BUG_ON(sizeof(XSavePKRU) != 0x8);
>  typedef struct ExtSaveArea {
>      uint32_t feature, bits;
>      uint32_t offset, size;
> +    uint32_t need_align;
>  } ExtSaveArea;
> 
>  #define XSAVE_STATE_AREA_COUNT (XSTATE_PKRU_BIT + 1)
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index aa9e636800..47bc4d5c1a 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -5487,6 +5487,7 @@ 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;
>              }
>          }
>          break;
> diff --git a/target/i386/kvm/kvm-cpu.c b/target/i386/kvm/kvm-cpu.c
> index d95028018e..6c4c1c6f9d 100644
> --- a/target/i386/kvm/kvm-cpu.c
> +++ b/target/i386/kvm/kvm-cpu.c
> @@ -105,6 +105,9 @@ static void kvm_cpu_xsave_init(void)
>                  assert(esa->size == sz);
>                  esa->offset = kvm_arch_get_supported_cpuid(s, 0xd, i, R_EBX);
>              }
> +
> +            uint32_t ecx = kvm_arch_get_supported_cpuid(s, 0xd, i, R_ECX);
> +            esa->need_align = ecx & (1u << 1) ? 1 : 0;
>          }
>      }
>  }