[lkml]   [2019]   [Aug]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [patch 1/2] x86/mm/pti: Handle unaligned address gracefully in pti_clone_pagetable()

> On Aug 28, 2019, at 8:51 AM, Thomas Gleixner <> wrote:
> On Wed, 28 Aug 2019, Dave Hansen wrote:
>> On 8/28/19 7:24 AM, Thomas Gleixner wrote:
>>> From: Song Liu <>
>>> pti_clone_pmds() assumes that the supplied address is either:
>>> - properly PUD/PMD aligned
>>> or
>>> - the address is actually mapped which means that independent
>>> of the mapping level (PUD/PMD/PTE) the next higher mapping
>>> exist.
>>> If that's not the case the unaligned address can be incremented by PUD or
>>> PMD size wrongly. All callers supply mapped and/or aligned addresses, but
>>> for robustness sake, it's better to handle that case proper and to emit a
>>> warning.
>> Reviewed-by: Dave Hansen <>
>> Song, did you ever root-cause the performance regression? I thought
>> there were still some mysteries there.
> See Peter's series to rework the ftrace code patching ...

Thanks Thomas.

Yes, in summary, enabling ftrace or kprobe-on-ftrace causes the kernel
to split PMDs in kernel text mapping.

Related question: while Peter's patches fix it for 5.3 kernel, they don't
apply cleanly over 5.2 kernel (which we are using). So I wonder what is
the best solution for 5.2 kernel. May patch also fixes the issue:

How about we apply this patch to upstream 5.2 kernel?


 \ /
  Last update: 2019-08-28 19:59    [W:0.093 / U:0.664 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site