[PATCH] <sys/platform/x86.h>: Add Intel LAM support

[Siddhesh Poyarekar]

On 12/22/20 9:52 AM, H.J. Lu via Libc-alpha wrote:
> Add Intel Linear Address Masking (LAM) support to <sys/platform/x86.h>.
> ---
>   manual/platform.texi               | 3 +++
>   sysdeps/x86/sys/platform/x86.h     | 3 +++
>   sysdeps/x86/tst-get-cpu-features.c | 1 +
>   3 files changed, 7 insertions(+)

The change itself is fine, but please provide a summary in the commit 
message of what Intel LAM is and what these changes enable.

Thanks,
Siddhesh

> diff --git a/manual/platform.texi b/manual/platform.texi
> index 8fec2933d6..b67683aeb3 100644
> --- a/manual/platform.texi
> +++ b/manual/platform.texi
> @@ -377,6 +377,9 @@ the indirect branch predictor barrier (IBPB).
>   @item
>   @code{KL} -- AES Key Locker instructions.
>   
> +@item
> +@code{LAM} -- Linear Address Masking.
> +
>   @item
>   @code{L1D_FLUSH} -- IA32_FLUSH_CMD MSR.
>   
> diff --git a/sysdeps/x86/sys/platform/x86.h b/sysdeps/x86/sys/platform/x86.h
> index 3ef92b04e8..99d8c9b0ab 100644
> --- a/sysdeps/x86/sys/platform/x86.h
> +++ b/sysdeps/x86/sys/platform/x86.h
> @@ -317,6 +317,7 @@ extern const struct cpu_features *__x86_get_cpu_features (unsigned int)
>   #define bit_cpu_FSRS		(1u << 11)
>   #define bit_cpu_FSRCS		(1u << 12)
>   #define bit_cpu_HRESET		(1u << 22)
> +#define bit_cpu_LAM		(1u << 26)
>   
>   /* COMMON_CPUID_INDEX_19.  */
>   
> @@ -541,6 +542,7 @@ extern const struct cpu_features *__x86_get_cpu_features (unsigned int)
>   #define index_cpu_FSRS		COMMON_CPUID_INDEX_7_ECX_1
>   #define index_cpu_FSRCS		COMMON_CPUID_INDEX_7_ECX_1
>   #define index_cpu_HRESET	COMMON_CPUID_INDEX_7_ECX_1
> +#define index_cpu_LAM		COMMON_CPUID_INDEX_7_ECX_1
>   
>   /* COMMON_CPUID_INDEX_19.  */
>   
> @@ -765,6 +767,7 @@ extern const struct cpu_features *__x86_get_cpu_features (unsigned int)
>   #define reg_FSRS		eax
>   #define reg_FSRCS		eax
>   #define reg_HRESET		eax
> +#define reg_LAM			eax
>   
>   /* COMMON_CPUID_INDEX_19.  */
>   
> diff --git a/sysdeps/x86/tst-get-cpu-features.c b/sysdeps/x86/tst-get-cpu-features.c
> index 667aa27117..6f1e925a6a 100644
> --- a/sysdeps/x86/tst-get-cpu-features.c
> +++ b/sysdeps/x86/tst-get-cpu-features.c
> @@ -227,6 +227,7 @@ do_test (void)
>     CHECK_CPU_FEATURE (FSRS);
>     CHECK_CPU_FEATURE (FSRCS);
>     CHECK_CPU_FEATURE (HRESET);
> +  CHECK_CPU_FEATURE (LAM);
>     CHECK_CPU_FEATURE (AESKLE);
>     CHECK_CPU_FEATURE (WIDE_KL);
>   
>