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Re: [PATCH v4 1/2] x86/ucode/AMD: apply the patch early on every logical thread
- To: Sergey Dyasli <sergey.dyasli@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 21 Feb 2023 14:57:24 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 21 Feb 2023 13:57:31 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 15.02.2023 16:38, Sergey Dyasli wrote:
> The original issue has been reported on AMD Bulldozer-based CPUs where
> ucode loading loses the LWP feature bit in order to gain the IBPB bit.
> LWP disabling is per-SMT/CMT core modification and needs to happen on
> each sibling thread despite the shared microcode engine. Otherwise,
> logical CPUs will end up with different cpuid capabilities.
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=216211
>
> Guests running under Xen happen to be not affected because of levelling
> logic for the feature masking/override MSRs which causes the LWP bit to
> fall out and hides the issue. The latest recommendation from AMD, after
> discussing this bug, is to load ucode on every logical CPU.
>
> In Linux kernel this issue has been addressed by e7ad18d1169c
> ("x86/microcode/AMD: Apply the patch early on every logical thread").
> Follow the same approach in Xen.
>
> Introduce SAME_UCODE match result and use it for early AMD ucode
> loading. Take this opportunity and move opt_ucode_allow_same out of
> compare_revisions() to the relevant callers and also modify the warning
> message based on it. Intel's side of things is modified for consistency
> but provides no functional change.
>
> Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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