Re: [PATCH v2 2/2] accel/mshv: enable amx tiles support for guests

[Magnus Kulke <magnuskulke@linux.microsoft.com>]

On Tue, Sep 22, 2026 at 05:21:56PM +0300, Doru Blânzeanu wrote:
> The AMX tiles feature uses a larger than 4kB area in xsave.
> This fix removes the code that disables AMX tiles in the partition and it
> adjusts the supported CPUID to advertise AMX tiles.
> 
> Signed-off-by: Doru Blânzeanu <dblanzeanu@linux.microsoft.com>
> ---
>  accel/mshv/mshv-all.c       | 18 +++++-------------
>  target/i386/mshv/mshv-cpu.c | 16 ----------------
>  2 files changed, 5 insertions(+), 29 deletions(-)
> 
> diff --git a/accel/mshv/mshv-all.c b/accel/mshv/mshv-all.c
> index 725ccd0511..99b2b3362a 100644
> --- a/accel/mshv/mshv-all.c
> +++ b/accel/mshv/mshv-all.c
> @@ -187,7 +187,6 @@ static int create_partition(int mshv_fd, int *vm_fd)
>  {
>      int ret;
>      uint64_t pt_flags, host_proc_features;
> -    union hv_partition_processor_xsave_features disabled_xsave_features;
>      union hv_partition_processor_features disabled_partition_features = {0};
>  
>      struct mshv_create_partition_v2 args = {0};
> @@ -200,17 +199,6 @@ static int create_partition(int mshv_fd, int *vm_fd)
>                 (1ULL << MSHV_PT_BIT_GPA_SUPER_PAGES) |
>                 (1ULL << MSHV_PT_BIT_CPU_AND_XSAVE_FEATURES);
>  
> -    /* enable all */
> -    disabled_xsave_features.as_uint64 = 0;
> -    /*
> -     * AMX TILE XSAVE state (XTILE_DATA) is 8KB, which exceeds the
> -     * current fixed 4KB XSAVE buffer size.
> -     */
> -    disabled_xsave_features.amx_tile_support = 1;
> -    disabled_xsave_features.amx_bf16_support = 1;
> -    disabled_xsave_features.amx_int8_support = 1;
> -    disabled_xsave_features.amx_fp16_support = 1;
> -
>      /*
>       * query host for supported processor features and disable unsupported
>       * features: (0 means supported, 1 means disabled, hence the negation)
> @@ -238,10 +226,14 @@ static int create_partition(int mshv_fd, int *vm_fd)
>      args.pt_cpu_fbanks[0] |= disabled_partition_features.as_uint64[0];
>      args.pt_cpu_fbanks[1] |= disabled_partition_features.as_uint64[1];
>  
> +    /*
> +     * for now, all the xsave features are enabled, the filtering is only done
> +     * at the CPUID level
> +     * TODO: filter the xsave features based on the CPUID derived from Cpu model
> +     */
>      /* populate args structure */
>      args.pt_flags = pt_flags;
>      args.pt_isolation = MSHV_PT_ISOLATION_NONE;
> -    args.pt_disabled_xsave = disabled_xsave_features.as_uint64;
>      args.pt_num_cpu_fbanks = MSHV_NUM_CPU_FEATURES_BANKS;
>  
>      ret = ioctl(mshv_fd, MSHV_CREATE_PARTITION, &args);
> diff --git a/target/i386/mshv/mshv-cpu.c b/target/i386/mshv/mshv-cpu.c
> index 5b845b3e4e..21a3534578 100644
> --- a/target/i386/mshv/mshv-cpu.c
> +++ b/target/i386/mshv/mshv-cpu.c
> @@ -2234,22 +2234,6 @@ uint32_t mshv_get_supported_cpuid(uint32_t func, uint32_t idx, int reg)
>           */
>          ret &= ~CPUID_7_0_ECX_LA57;
>      }
> -    if (func == 0x07 && idx == 0 && reg == R_EDX) {
> -        /*
> -         * AMX TILE XSAVE state (XTILE_DATA) is 8KB, which exceeds the
> -         * current fixed 4KB XSAVE buffer size. Filter until buffer
> -         * sizing is computed dynamically from CPUID.
> -         */
> -        ret &= ~CPUID_7_0_EDX_AMX_TILE;
> -        ret &= ~CPUID_7_0_EDX_AMX_BF16;
> -        ret &= ~CPUID_7_0_EDX_AMX_INT8;
> -    }
> -    if (func == 0x07 && idx == 1 && reg == R_EAX) {
> -        ret &= ~CPUID_7_1_EAX_AMX_FP16;
> -    }
> -    if (func == 0x07 && idx == 1 && reg == R_EDX) {
> -        ret &= ~CPUID_7_1_EDX_AMX_COMPLEX;
> -    }
>  
>      return ret;
>  }
> -- 
> 2.53.0

Reviewed-by: Magnus Kulke <magnuskulke@linux.microsoft.com>