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SubjectRe: [PATCH 0/3] Use global pages with PTI
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On 02/15/2018 09:47 AM, Linus Torvalds wrote:
> On Thu, Feb 15, 2018 at 5:20 AM, Dave Hansen
> <dave.hansen@linux.intel.com> wrote:
>>
>> During the switch over to PTI, we seem to have lost our ability to have
>> GLOBAL mappings.
>
> Oops. Odd, I have this distinct memory of somebody even _testing_ the
> global bit performance when I pointed out that we shouldn't just make
> the bit go away entirely.
>
> [ goes back and looks at archives ]
>
> Oh, that was in fact you who did that performance test.
...
> Did you perhaps re-run any benchmark numbers just to verify? Because
> it's always good to back up patches that should improve performance
> with actual numbers..

Nope, haven't done it yet, but I will.

I wanted to double-check that there was not a reason for doing the
global disabling other than the K8 TLB mismatch issues that Thomas fixed
a few weeks ago:

> commit 52994c256df36fda9a715697431cba9daecb6b11
> Author: Thomas Gleixner <tglx@linutronix.de>
> Date: Wed Jan 3 15:57:59 2018 +0100
>
> x86/pti: Make sure the user/kernel PTEs match
>
> Meelis reported that his K8 Athlon64 emits MCE warnings when PTI is
> enabled:
>
> [Hardware Error]: Error Addr: 0x0000ffff81e000e0
> [Hardware Error]: MC1 Error: L1 TLB multimatch.
> [Hardware Error]: cache level: L1, tx: INSN

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