Re: [PATCH v10 05/50] x86/speculation: Do not enable Automatic IBRS if SEV SNP is enabled

[Borislav Petkov]

On Mon, Oct 16, 2023 at 08:27:34AM -0500, Michael Roth wrote:
> From: Kim Phillips <kim.phillips@xxxxxxx>
> 
> Without SEV-SNP, Automatic IBRS protects only the kernel. But when
> SEV-SNP is enabled, the Automatic IBRS protection umbrella widens to all
> host-side code, including userspace. This protection comes at a cost:
> reduced userspace indirect branch performance.
> 
> To avoid this performance loss, don't use Automatic IBRS on SEV-SNP
> hosts. Fall back to retpolines instead.
> 
> Signed-off-by: Kim Phillips <kim.phillips@xxxxxxx>
> [mdr: squash in changes from review discussion]
> Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
> ---
>  arch/x86/kernel/cpu/common.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)

Acked-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>

-- 
Regards/Gruss,
    Boris.

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