Re: [PATCH v2] x86/bugs: Warn when "ibrs" mitigation is selected on Enhanced IBRS parts

On Thu, Jul 14, 2022 at 09:11:18PM -0300, Thadeu Lima de Souza Cascardo wrote:

On Thu, Jul 14, 2022 at 04:15:35PM -0700, Pawan Gupta wrote:

...

IBRS mitigation for spectre_v2 forces write to MSR_IA32_SPEC_CTRL at every kernel entry/exit. On Enhanced IBRS parts setting MSR_IA32_SPEC_CTRL[IBRS] only once at boot is sufficient. MSR writes at every kernel entry/exit incur unnecessary performance loss.

When Enhanced IBRS feature is present, print a warning about this unnecessary performance loss.

Signed-off-by: Pawan Gupta pawan.kumar.gupta@linux.intel.com

Reviewed-by: Thadeu Lima de Souza Cascardo cascardo@canonical.com

Thanks for the review.

Pawan