linux-kernel - Re: [tip: x86/urgent] x86/mm: Fix pti_clone_entry

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Message-ID: <d99175bb-b5ca-46e6-a781-df4d21e9b7a8@roeck-us.net>
Date: Tue, 6 Aug 2024 07:25:42 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
 x86@...nel.org
Subject: Re: [tip: x86/urgent] x86/mm: Fix pti_clone_entry_text() for i386

On 8/6/24 01:50, Peter Zijlstra wrote:
> On Mon, Aug 05, 2024 at 09:52:06PM -0700, Guenter Roeck wrote:
>> Hi Peter,
>>
>> On Thu, Aug 01, 2024 at 10:55:31AM -0000, tip-bot2 for Peter Zijlstra wrote:
>>> The following commit has been merged into the x86/urgent branch of tip:
>>>
>>> Commit-ID:     49947e7aedfea2573bada0c95b85f6c2363bef9f
>>> Gitweb:        https://git.kernel.org/tip/49947e7aedfea2573bada0c95b85f6c2363bef9f
>>> Author:        Peter Zijlstra <peterz@...radead.org>
>>> AuthorDate:    Thu, 01 Aug 2024 12:42:25 +02:00
>>> Committer:     Peter Zijlstra <peterz@...radead.org>
>>> CommitterDate: Thu, 01 Aug 2024 12:48:23 +02:00
>>>
>>> x86/mm: Fix pti_clone_entry_text() for i386
>>>
>>> While x86_64 has PMD aligned text sections, i386 does not have this
>>> luxery. Notably ALIGN_ENTRY_TEXT_END is empty and _etext has PAGE
>>> alignment.
>>>
>>> This means that text on i386 can be page granular at the tail end,
>>> which in turn means that the PTI text clones should consistently
>>> account for this.
>>>
>>> Make pti_clone_entry_text() consistent with pti_clone_kernel_text().
>>>
>>> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>>
>> With this patch in the tree, some of my qemu tests (those with PAE enabled)
>> report several WARNING backtraces.
>>
>> WARNING: CPU: 0 PID: 1 at arch/x86/mm/pti.c:256 pti_clone_pgtable+0x298/0x2dc
>>
>> WARNING: CPU: 0 PID: 1 at arch/x86/mm/pti.c:394 pti_clone_pgtable+0x29a/0x2dc
>>
>> The backtraces are repeated multiple times.
>>
>> Please see
>>
>> https://kerneltests.org/builders/qemu-x86-master/builds/253/steps/qemubuildcommand/logs/stdio
>>
>> for complete logs.
> 
> Could you try the below patch? If that don't work, could you provide the
> .config, I'm assuming that'll work with the bits I grabbed last time.
> 

Unfortunately that makes it worse: It causes qemu to quit immediately
without logging anything.

I created http://server.roeck-us.net/qemu/x86-v6.11-rc2/ with all
the relevant information. Please let me know if you need anything else.

Thanks,
Guenter