Re: [PATCH v10 08/38] x86/cpufeatures: Add the cpu feature bit for FRED

[Juergen Gross]

On 14.09.23 06:47, Xin Li wrote:

From: "H. Peter Anvin (Intel)" <h...@zytor.com>

Any FRED CPU will always have the following features as its baseline:
   1) LKGS, load attributes of the GS segment but the base address into
      the IA32_KERNEL_GS_BASE MSR instead of the GS segment’s descriptor
      cache.
   2) WRMSRNS, non-serializing WRMSR for faster MSR writes.

Signed-off-by: H. Peter Anvin (Intel) <h...@zytor.com>
Tested-by: Shan Kang <shan.k...@intel.com>
Signed-off-by: Xin Li <xin3...@intel.com>

In order to avoid having to add paravirt support for FRED I think
xen_init_capabilities() should gain:

+    setup_clear_cpu_cap(X86_FEATURE_FRED);


Juergen

---
  arch/x86/include/asm/cpufeatures.h       | 1 +
  arch/x86/kernel/cpu/cpuid-deps.c         | 2 ++
  tools/arch/x86/include/asm/cpufeatures.h | 1 +
  3 files changed, 4 insertions(+)

diff --git a/arch/x86/include/asm/cpufeatures.h 
b/arch/x86/include/asm/cpufeatures.h
index 330876d34b68..57ae93dc1e52 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -321,6 +321,7 @@
  #define X86_FEATURE_FZRM              (12*32+10) /* "" Fast zero-length REP 
MOVSB */
  #define X86_FEATURE_FSRS              (12*32+11) /* "" Fast short REP STOSB */
  #define X86_FEATURE_FSRC              (12*32+12) /* "" Fast short REP 
{CMPSB,SCASB} */
+#define X86_FEATURE_FRED               (12*32+17) /* Flexible Return and Event 
Delivery */
  #define X86_FEATURE_LKGS              (12*32+18) /* "" Load "kernel" 
(userspace) GS */
  #define X86_FEATURE_WRMSRNS           (12*32+19) /* "" Non-Serializing Write 
to Model Specific Register instruction */
  #define X86_FEATURE_AMX_FP16          (12*32+21) /* "" AMX fp16 Support */
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index e462c1d3800a..b7174209d855 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -82,6 +82,8 @@ static const struct cpuid_dep cpuid_deps[] = {
        { X86_FEATURE_XFD,                      X86_FEATURE_XGETBV1   },
        { X86_FEATURE_AMX_TILE,                 X86_FEATURE_XFD       },
        { X86_FEATURE_SHSTK,                    X86_FEATURE_XSAVES    },
+       { X86_FEATURE_FRED,                     X86_FEATURE_LKGS      },
+       { X86_FEATURE_FRED,                     X86_FEATURE_WRMSRNS   },
        {}
  };

index 1b9d86ba5bc2..18bab7987d7f 100644
--- a/tools/arch/x86/include/asm/cpufeatures.h
+++ b/tools/arch/x86/include/asm/cpufeatures.h
@@ -317,6 +317,7 @@
  #define X86_FEATURE_FZRM              (12*32+10) /* "" Fast zero-length REP 
MOVSB */
  #define X86_FEATURE_FSRS              (12*32+11) /* "" Fast short REP STOSB */
  #define X86_FEATURE_FSRC              (12*32+12) /* "" Fast short REP 
{CMPSB,SCASB} */
+#define X86_FEATURE_FRED               (12*32+17) /* Flexible Return and Event 
Delivery */
  #define X86_FEATURE_LKGS              (12*32+18) /* "" Load "kernel" 
(userspace) GS */
  #define X86_FEATURE_WRMSRNS           (12*32+19) /* "" Non-Serializing Write 
to Model Specific Register instruction */
  #define X86_FEATURE_AMX_FP16          (12*32+21) /* "" AMX fp16 Support */

diff --git a/tools/arch/x86/include/asm/cpufeatures.h b/tools/arch/x86/include/asm/cpufeatures.h

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