Re: [PATCH 3/5] x86/spec-ctrl: Remove open-coded check of SVM_FEATURE_SPEC_CTRL

[Jan Beulich]

On 29.04.2024 17:16, Andrew Cooper wrote:
> Now that the SVM feature leaf has been included in normal feature handling, it
> is available early enough for init_speculation_mitigations() to use.
> 
> No functional change.
> 
> Signed-off-by: Andrew Cooper 

Reviewed-by: Jan Beulich 
even if ...

> --- a/xen/arch/x86/include/asm/cpufeature.h
> +++ b/xen/arch/x86/include/asm/cpufeature.h
> @@ -217,6 +217,9 @@ static inline bool boot_cpu_has(unsigned int feat)
>  #define cpu_has_rfds_no boot_cpu_has(X86_FEATURE_RFDS_NO)
>  #define cpu_has_rfds_clear  boot_cpu_has(X86_FEATURE_RFDS_CLEAR)
>  
> +/* CPUID level 0x800a.edx */
> +#define cpu_has_v_spec_ctrl boot_cpu_has(X86_FEATURE_V_SPEC_CTRL)

... the names here were to change (see comment on the earlier patch). In
fact ...

> @@ -1896,12 +1895,8 @@ void __init init_speculation_mitigations(void)
>   *
>   * No need for SCF_ist_sc_msr because Xen's value is restored
>   * atomically WRT NMIs in the VMExit path.
> - *
> - * TODO: Adjust cpu_has_svm_spec_ctrl to be usable earlier on boot.
>   */
> -if ( opt_msr_sc_hvm &&
> - (boot_cpu_data.extended_cpuid_level >= 0x800aU) &&
> - (cpuid_edx(0x800aU) & (1u << SVM_FEATURE_SPEC_CTRL)) )
> +if ( opt_msr_sc_hvm && cpu_has_v_spec_ctrl )
>  setup_force_cpu_cap(X86_FEATURE_SC_MSR_HVM);
>  }

... the use here demonstrates my earlier point quite well: It being AMD's
feature is completely invisible here when not considering the code being
replaced. But yes, when looking at the entire comment / block, it still
is visible.

Jan

[PATCH 3/5] x86/spec-ctrl: Remove open-coded check of SVM_FEATURE_SPEC_CTRL

[Andrew Cooper]

Now that the SVM feature leaf has been included in normal feature handling, it
is available early enough for init_speculation_mitigations() to use.

No functional change.

Signed-off-by: Andrew Cooper 
---
CC: Jan Beulich 
CC: Roger Pau Monné 
CC: Stefano Stabellini 
CC: Xenia Ragiadakou 
CC: Sergiy Kibrik 
CC: George Dunlap 
CC: Andrei Semenov 
CC: Vaishali Thakkar 
---
 xen/arch/x86/include/asm/cpufeature.h | 3 +++
 xen/arch/x86/spec_ctrl.c  | 7 +--
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/include/asm/cpufeature.h 
b/xen/arch/x86/include/asm/cpufeature.h
index 9bc553681f4a..77cfd900cb56 100644
--- a/xen/arch/x86/include/asm/cpufeature.h
+++ b/xen/arch/x86/include/asm/cpufeature.h
@@ -217,6 +217,9 @@ static inline bool boot_cpu_has(unsigned int feat)
 #define cpu_has_rfds_no boot_cpu_has(X86_FEATURE_RFDS_NO)
 #define cpu_has_rfds_clear  boot_cpu_has(X86_FEATURE_RFDS_CLEAR)
 
+/* CPUID level 0x800a.edx */
+#define cpu_has_v_spec_ctrl boot_cpu_has(X86_FEATURE_V_SPEC_CTRL)
+
 /* Synthesized. */
 #define cpu_has_arch_perfmonboot_cpu_has(X86_FEATURE_ARCH_PERFMON)
 #define cpu_has_cpuid_faulting  boot_cpu_has(X86_FEATURE_CPUID_FAULTING)
diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index 40f6ae017010..0bda9d01def5 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -11,7 +11,6 @@
 #include 
 
 #include 
-#include 
 #include 
 #include 
 #include 
@@ -1896,12 +1895,8 @@ void __init init_speculation_mitigations(void)
  *
  * No need for SCF_ist_sc_msr because Xen's value is restored
  * atomically WRT NMIs in the VMExit path.
- *
- * TODO: Adjust cpu_has_svm_spec_ctrl to be usable earlier on boot.
  */
-if ( opt_msr_sc_hvm &&
- (boot_cpu_data.extended_cpuid_level >= 0x800aU) &&
- (cpuid_edx(0x800aU) & (1u << SVM_FEATURE_SPEC_CTRL)) )
+if ( opt_msr_sc_hvm && cpu_has_v_spec_ctrl )
 setup_force_cpu_cap(X86_FEATURE_SC_MSR_HVM);
 }
 
-- 
2.30.2