Re: [Qemu-devel][PATCH v5 2/4] x86/cpuid: Add XSAVES feature words and CET related state bits

[Xiaoyao Li]

On 5/10/2020 9:42 AM, Yang Weijiang wrote:
> CET SHSTK/IBT MSRs can be saved/restored with XSAVES/XRSTORS, but
> currently the related feature words are not supported, so add the
> new entries. XSAVES/RSTORS always use compacted storage format, which
> means the supervisor states' offsets are always 0, ignore them while
> calculating stardard format storage size.
>
> Signed-off-by: Zhang Yi <yi.z.zhang@linux.intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> ---
>   target/i386/cpu.c | 38 ++++++++++++++++++++++++++++++++++++--
>   1 file changed, 36 insertions(+), 2 deletions(-)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 90ffc5f3b1..3174e05482 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -965,7 +965,7 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
>           .type = CPUID_FEATURE_WORD,
>           .feat_names = {
>               NULL, "avx512vbmi", "umip", "pku",
> -            NULL /* ospke */, "waitpkg", "avx512vbmi2", NULL,
> +            NULL /* ospke */, "waitpkg", "avx512vbmi2", "shstk",
>               "gfni", "vaes", "vpclmulqdq", "avx512vnni",
>               "avx512bitalg", NULL, "avx512-vpopcntdq", NULL,
>               "la57", NULL, NULL, NULL,
> @@ -988,7 +988,7 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
>               NULL, NULL, "md-clear", NULL,
>               NULL, NULL, NULL, NULL,
>               NULL, NULL, NULL /* pconfig */, NULL,
> -            NULL, NULL, NULL, NULL,
> +            "ibt", NULL, NULL, NULL,
>               NULL, NULL, "spec-ctrl", "stibp",
>               NULL, "arch-capabilities", "core-capability", "ssbd",
>           },
> @@ -1069,6 +1069,26 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] 
> = {
>           },
>           .tcg_features = TCG_XSAVE_FEATURES,
>       },
> +    /* Below are xsaves feature words */
> +    [FEAT_XSAVES_LO] = {
> +        .type = CPUID_FEATURE_WORD,
> +        .cpuid = {
> +            .eax = 0xD,
> +            .needs_ecx = true,
> +            .ecx = 1,
> +            .reg = R_ECX,
> +        },
> +        .migratable_flags = XSTATE_CET_U_MASK,

why exclude XSTATE_CET_S_MASK? Is any reason why it not migratable?

> +    },
> +    [FEAT_XSAVES_HI] = {
> +        .type = CPUID_FEATURE_WORD,
> +        .cpuid = {
> +            .eax = 0xD,
> +            .needs_ecx = true,
> +            .ecx = 1,
> +            .reg = R_EDX
> +        },
> +    },
>       [FEAT_6_EAX] = {
>           .type = CPUID_FEATURE_WORD,
>           .feat_names = {
> @@ -1455,6 +1475,14 @@ static const ExtSaveArea x86_ext_save_areas[] = {
>             { .feature = FEAT_7_0_ECX, .bits = CPUID_7_0_ECX_PKU,
>               .offset = offsetof(X86XSaveArea, pkru_state),
>               .size = sizeof(XSavePKRU) },
> +    [XSTATE_CET_U_BIT] = {
> +            .feature = FEAT_7_0_ECX, .bits = CPUID_7_0_ECX_CET_SHSTK,
> +            .offset = 0 /*supervisor mode component, offset = 0 */,
> +            .size = sizeof(XSavesCETU) },
> +    [XSTATE_CET_S_BIT] = {
> +            .feature = FEAT_7_0_ECX, .bits = CPUID_7_0_ECX_CET_SHSTK,
> +            .offset = 0 /*supervisor mode component, offset = 0 */,
> +            .size = sizeof(XSavesCETS) },
>   };
>   
>   static uint32_t xsave_area_size(uint64_t mask)
> @@ -1465,6 +1493,9 @@ static uint32_t xsave_area_size(uint64_t mask)
>       for (i = 0; i < ARRAY_SIZE(x86_ext_save_areas); i++) {
>           const ExtSaveArea *esa = &x86_ext_save_areas[i];
>           if ((mask >> i) & 1) {
> +            if (i >= 2 && !esa->offset) {
> +                continue;
> +            }
>               ret = MAX(ret, esa->offset + esa->size);
>           }
>       }
> @@ -6008,6 +6039,9 @@ static void x86_cpu_reset(DeviceState *dev)
>       }
>       for (i = 2; i < ARRAY_SIZE(x86_ext_save_areas); i++) {
>           const ExtSaveArea *esa = &x86_ext_save_areas[i];
> +        if (!esa->offset) {
> +            continue;
> +        }
>           if (env->features[esa->feature] & esa->bits) {
>               xcr0 |= 1ull << i;
>           }