linux-kernel - Re: [PATCH] mm: fix up a spurious page fault whenever it happens

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Message-ID: <519D11BF.5000604@redhat.com>
Date:	Wed, 22 May 2013 14:43:11 -0400
From:	Rik van Riel <riel@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Stanislav Meduna <stano@...una.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Hai Huang <hhuang@...hat.com>
Subject: Re: [PATCH] mm: fix up a spurious page fault whenever it happens

On 05/22/2013 02:42 PM, H. Peter Anvin wrote:
> On 05/22/2013 11:35 AM, Rik van Riel wrote:
>> On 05/22/2013 02:21 PM, Stanislav Meduna wrote:
>>> On 22.05.2013 20:11, Steven Rostedt wrote:
>>>
>>>> Did you apply both patches? Without the first one, this one is
>>>> meaningless.
>>>
>>> Sure.
>>>
>>> BTW, back when I tried to pinpoint it I also tried adding
>>>     flush_tlb_page(vma, address)
>>> at the beginning of handle_pte_fault, which as I read should
>>> be basically the same. It did not not change anything.
>>
>> I'm stumped.
>>
>> If the Geode knows how to flush single TLB entries, it
>> should do that when flush_tlb_page is called.
>>
>> If it does not know, it should throw an invalid instruction
>> exception, and not quietly complete the instruction without
>> doing anything.
>>
>
> Some CPUs have had errata when it comes to flushing large pages that
> have been split into small pages by hardware, e.g. due to MTRR
> conflicts.  In that case, fragments of the large page may have been left
> in the TLB.
>
> Could that explain what you are seeing?

That would be testable by changing __native_flush_tlb_single()
to call __flush_tlb(), instead of doing an invlpg instruction.

In other words, make the code look like this, for testing:

static inline void __native_flush_tlb_single(unsigned long addr)
{
         __flush_tlb();
}

This on top of the other two patches.
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