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Re: [PATCH 6/6] x86/boot: Expose MSR_ARCH_CAPS data in guest max policies
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 16 May 2023 16:58:02 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 16 May 2023 14:58:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 15.05.2023 16:42, Andrew Cooper wrote:
> --- a/xen/arch/x86/cpu-policy.c
> +++ b/xen/arch/x86/cpu-policy.c
> @@ -408,6 +408,25 @@ static void __init calculate_host_policy(void)
> p->platform_info.cpuid_faulting = cpu_has_cpuid_faulting;
> }
>
> +static void __init guest_common_max_feature_adjustments(uint32_t *fs)
> +{
> + if ( boot_cpu_data.x86_vendor == X86_VENDOR_INTEL )
> + {
> + /*
> + * MSR_ARCH_CAPS is just feature data, and we can offer it to guests
> + * unconditionally, although limit it to Intel systems as it is
> highly
> + * uarch-specific.
> + *
> + * In particular, the RSBA and RRSBA bits mean "you might migrate to
> a
> + * system where RSB underflow uses alternative predictors (a.k.a
> + * Retpoline not safe)", so these need to be visible to a guest in
> all
> + * cases, even when it's only some other server in the pool which
> + * suffers the identified behaviour.
> + */
> + __set_bit(X86_FEATURE_ARCH_CAPS, fs);
> + }
> +}
Wouldn't this better be accompanied by marking the bit !a in the public header?
Jan
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