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Re: [PATCH 1/3] x86/msr: Split MSR_SPEC_CTRL handling
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Fri, 14 Jan 2022 12:03:57 +0100
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Wei Liu <wl@xxxxxxx>
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Thu, Jan 13, 2022 at 04:38:31PM +0000, Andrew Cooper wrote:
> In order to fix a VT-x bug, and support MSR_SPEC_CTRL on AMD, there will need
> to be three different access methods for where the guest's value lives.
> However, it would be better not to duplicate the #GP checking logic.
>
> guest_{rd,wr}msr() are always called first in the PV and HVM MSR paths, so we
> can repurpose X86EMUL_UNHANDLEABLE slightly for this. This is going to be a
> common pattern for other MSRs too in the future.
>
> Duplicate the msrs->spec_ctrl.raw accesses in the PV and VT-x paths for now.
> The SVM path is currently unreachable because of the CPUID policy.
>
> No functional change.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
It feels a bit weird to have the checks separated from the actual
access to the MSR data, but that's likely better than to replicate the
checks in both the PV and HVM vendor paths.
Thanks, Roger.
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