From: Song Liu <songliubraving@fb.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>, Joerg Roedel <jroedel@suse.de>,
"Andy Lutomirski" <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
"Rik van Riel" <riel@surriel.com>
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 [thread overview]
Message-ID: <309E5006-E869-4761-ADE2-ADB7A1A63FF1@fb.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1908281750410.1938@nanos.tec.linutronix.de>
> 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
next prev parent reply other threads:[~2019-08-28 17:59 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-28 14:24 [patch 0/2] x86/mm/pti: Robustness updates Thomas Gleixner
2019-08-28 14:24 ` [patch 1/2] x86/mm/pti: Handle unaligned address gracefully in pti_clone_pagetable() Thomas Gleixner
2019-08-28 15:46 ` Dave Hansen
2019-08-28 15:51 ` Thomas Gleixner
2019-08-28 17:58 ` Song Liu [this message]
2019-08-28 20:05 ` Thomas Gleixner
2019-08-28 20:32 ` Song Liu
2019-08-28 22:31 ` [PATCH] x86/mm/cpa: Prevent large page split when ftrace flips RW on kernel text Thomas Gleixner
2019-08-28 23:03 ` Song Liu
2019-08-29 13:01 ` Peter Zijlstra
2019-08-29 18:55 ` [tip: x86/urgent] " tip-bot2 for Thomas Gleixner
2019-08-28 18:58 ` [patch 1/2] x86/mm/pti: Handle unaligned address gracefully in pti_clone_pagetable() Ingo Molnar
2019-08-28 19:45 ` Thomas Gleixner
2019-08-28 20:54 ` [patch V2 " Thomas Gleixner
2019-08-28 21:52 ` Thomas Gleixner
2019-08-28 21:54 ` [patch V3 " Thomas Gleixner
2019-08-28 23:22 ` Ingo Molnar
2019-08-29 19:02 ` [tip: x86/pti] " tip-bot2 for Song Liu
2019-08-30 10:24 ` [patch V3 1/2] " Joerg Roedel
2019-08-28 14:24 ` [patch 2/2] x86/mm/pti: Do not invoke PTI functions when PTI is disabled Thomas Gleixner
2019-08-28 15:47 ` Dave Hansen
2019-08-28 17:49 ` Song Liu
2019-08-28 19:00 ` Ingo Molnar
2019-08-29 19:02 ` [tip: x86/pti] " tip-bot2 for Thomas Gleixner
2019-08-30 10:25 ` [patch 2/2] " Joerg Roedel
2019-08-28 16:03 ` [patch 0/2] x86/mm/pti: Robustness updates Peter Zijlstra
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