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Re: [XEN PATCH v2 2/5] x86/amd: configurable handling of AMD-specific MSRs access
- To: Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 19 Aug 2024 14:21:28 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 19 Aug 2024 12:21:37 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16.08.2024 13:12, Sergiy Kibrik wrote:
> Do not compile handlers of guest access to AMD-specific MSRs when
> CONFIG_AMD=n.
What I'm missing in the description is clarification on how boundaries were
drawn. In guest_rdmsr() there is, for example, also handling of
MSR_AMD_PATCHLEVEL.
Which I'm okay to leave aside for now, as long as it's clear why that is.
> --- a/xen/arch/x86/msr.c
> +++ b/xen/arch/x86/msr.c
> @@ -219,6 +219,7 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t
> *val)
> *val = msrs->tsc_aux;
> break;
>
> +#ifdef CONFIG_AMD
> case MSR_K8_SYSCFG:
> case MSR_K8_TOP_MEM1:
> case MSR_K8_TOP_MEM2:
> @@ -281,6 +282,7 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t
> *val)
> ? 0 : (msr - MSR_AMD64_DR1_ADDRESS_MASK +
> 1),
> ARRAY_SIZE(msrs->dr_mask))];
> break;
> +#endif /* CONFIG_AMD */
>
> /*
> * TODO: Implement when we have better topology representation.
> @@ -552,6 +554,7 @@ int guest_wrmsr(struct vcpu *v, uint32_t msr, uint64_t
> val)
> wrmsr_tsc_aux(val);
> break;
>
> +#ifdef CONFIG_AMD
> case MSR_VIRT_SPEC_CTRL:
> if ( !cp->extd.virt_ssbd )
> goto gp_fault;
> @@ -598,6 +601,7 @@ int guest_wrmsr(struct vcpu *v, uint32_t msr, uint64_t
> val)
> if ( v == curr && (curr->arch.dr7 & DR7_ACTIVE_MASK) )
> wrmsrl(msr, val);
> break;
> +#endif /* CONFIG_AMD */
>
> default:
> return X86EMUL_UNHANDLEABLE;
Is just adding #ifdef-s actually correct? That results in different behavior on
e.g. Intel hardware, I think, depending on whether AMD=y or AMD=n. In the latter
case the function will now return X86EMUL_UNHANDLEABLE, while in the former case
it would return X86EMUL_EXCEPTION.
Jan
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