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SubjectRe: [PATCH v2] x86/bugs: Warn when "ibrs" mitigation is selected on Enhanced IBRS parts
On Fri, Jul 15, 2022 at 07:25:43AM +0200, Greg KH 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>
> > ---
> > v1->v2: Instead of changing the mitigation, print a warning about the
> > perf loss.
> >
> > v1: https://lore.kernel.org/lkml/0456b35fb9ef957d9a9138e0913fb1a3fd445dff.1657747493.git.pawan.kumar.gupta@linux.intel.com/
> >
> > arch/x86/kernel/cpu/bugs.c | 3 +++
> > 1 file changed, 3 insertions(+)
>
> <formletter>
>
> This is not the correct way to submit patches for inclusion in the
> stable kernel tree. Please read:
> https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> for how to do this properly.
>
> </formletter>

Sorry, I CCed stable@ by mistake. This version just adds a warning, it
is not intended to be backported.

Thanks,
Pawan

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