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Message-ID: <6a43b05b-ffdd-0e6f-56a0-5b78532ee383@amd.com>
Date: Thu, 20 Jul 2023 16:53:23 -0500
From: Kim Phillips <kim.phillips@....com>
To: Jim Mattson <jmattson@...gle.com>
CC: <x86@...nel.org>, Tom Lendacky <thomas.lendacky@....com>,
Borislav Petkov <bp@...en8.de>,
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Subject: Re: [PATCH] x86/cpu: Enable STIBP if Automatic IBRS is enabled
On 7/20/23 3:58 PM, Jim Mattson wrote:
> On Thu, Jul 20, 2023 at 12:48 PM Kim Phillips <kim.phillips@....com> wrote:
>>
>> Unlike Intel's Enhanced IBRS feature, AMD's Automatic IBRS does not
>> provide protection to processes running at CPL3/user mode [1].
>>
>> Explicitly enable STIBP to protect against cross-thread CPL3
>> branch target injections on systems with Automatic IBRS enabled.
>
> Is there any performance penalty to enabling STIBP + AUTOIBRS, aside
> from the lost sharing?
Not to my knowledge.
> Or does this just effectively tag the branch
> prediction information with thread ID?
I don't know the implementation, but AFAIK, AUTOIBRS and STIBP
are independent of each other.
Thanks,
Kim
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