Re: [PATCH v3 1/6] cpu/bugs: Allow forcing Automatic IBRS with SNP active using spectre_v2=eibrs

[Pawan Gupta <pawan.kumar.gupta@linux.intel.com>]

On Thu, Apr 02, 2026 at 03:25:53PM -0500, Kim Phillips wrote:
> spectre_v2=eibrs currently enables retpolines when SNP is enabled,
> instead of AutoIBRS (EIBRS) because the commit that disabled
> AutoIBRS if SNP is enabled stopped short of enabling
> X86_FEATURE_IBRS_ENHANCED.
> 
> Change the logic to enable X86_FEATURE_IBRS_ENHANCED, and move the
> decision to switch to retpolines in the default/"auto" case in

The retpoline switch happens in force case(=on) too.

> spectre_v2_select_mitigation().  This allows the existing
> spectre_v2=eibrs logic to work as intended.
> 
> Also emit a performance loss warning for using AutoIBRS with
> SNP enabled.
> 
> Fixes: acaa4b5c4c85 ("x86/speculation: Do not enable Automatic IBRS if SEV-SNP is enabled")
> Reported-by: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Borislav Petkov (AMD) <bp@alien8.de>
> Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Sean Christopherson <seanjc@google.com>
> Cc: stable@kernel.org
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202603121136.bc8zNsHS-lkp@intel.com/
> Signed-off-by: Kim Phillips <kim.phillips@amd.com>
> ---

Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>