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Re: [PATCH 1/8] x86/msr: Fix migration compatibility issue with MSR_SPEC_CTRL
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 26 Jan 2022 17:33:40 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 26 Jan 2022 16:33:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 26.01.2022 09:44, Andrew Cooper wrote:
> This bug existed in early in 2018 between MSR_SPEC_CTRL arriving in microcode,
> and SSBD arriving a few months later. It went unnoticed presumably because
> everyone was busy rebooting everything.
>
> The same bug will reappear when adding PSFD support.
>
> Clamp the guest MSR_SPEC_CTRL value to that permitted by CPUID on migrate.
> The guest is already playing with reserved bits at this point, and clamping
> the value will prevent a migration to a less capable host from failing.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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