Messages in this thread | | | From | Song Liu <> | Subject | Re: [patch 1/2] x86/mm/pti: Handle unaligned address gracefully in pti_clone_pagetable() | Date | Wed, 28 Aug 2019 17:58:20 +0000 |
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> On Aug 28, 2019, at 8:51 AM, Thomas Gleixner <tglx@linutronix.de> wrote: > > On Wed, 28 Aug 2019, Dave Hansen wrote: >> On 8/28/19 7:24 AM, Thomas Gleixner wrote: >>> From: Song Liu <songliubraving@fb.com> >>> >>> 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 <dave.hansen@linux.intel.com> >> >> 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:
https://lore.kernel.org/lkml/20190823052335.572133-1-songliubraving@fb.com/
How about we apply this patch to upstream 5.2 kernel?
Thanks, Song
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