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Re: [PATCH 3/5] x86/spec-ctrl: Remove open-coded check of SVM_FEATURE_SPEC_CTRL
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 30 Apr 2024 15:13:51 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Xenia Ragiadakou <xenia.ragiadakou@xxxxxxx>, Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Andrei Semenov <andrei.semenov@xxxxxxxx>, Vaishali Thakkar <vaishali.thakkar@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 30 Apr 2024 13:14:03 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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 <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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 0x8000000a.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 >= 0x8000000aU) &&
> - (cpuid_edx(0x8000000aU) & (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
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