linux-kernel - Re: [PATCH v2 5/8] x86/mtrr: revert commit 90b926e68f50

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Date:   Mon, 13 Feb 2023 07:07:37 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Linux regressions mailing list <regressions@...ts.linux.dev>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     lists@...dbynature.de, mikelley@...rosoft.com,
        torvalds@...ux-foundation.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 5/8] x86/mtrr: revert commit 90b926e68f50

On 10.02.23 19:59, Linux regression tracking (Thorsten Leemhuis) wrote:
> Hi, this is your Linux kernel regression tracker.
> 
> On 09.02.23 08:22, Juergen Gross wrote:
>> Commit 90b926e68f50 ("x86/pat: Fix pat_x_mtrr_type() for MTRR disabled
>> case") has introduced a regression with Xen.
>>
>> Revert the patch.
> 
> That regression you refer to is afaics one I'm tracking[1] that was
> introduced this cycle. That makes me wonder: could this patch be applied
> directly to fix the issue quickly? Or are patches 1 to 4 needed as well
> (or the whole series?) to avoid other problems?

Patches 1-4 are needed, too, as otherwise the issue claimed to be fixed
with patch 5 would show up again.

I'm working on addressing the comments I've received.


Juergen

> 
> Ciao, Thorsten
> 
> [1]
> https://lore.kernel.org/all/4fe9541e-4d4c-2b2a-f8c8-2d34a7284930@nerdbynature.de/
> 
> P.S.: BTW; let me tell regzbot to monitor this thread:
> 
> #regzbot ^backmonitor:
> https://lore.kernel.org/all/4fe9541e-4d4c-2b2a-f8c8-2d34a7284930@nerdbynature.de/
> 
> 
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> ---
>>   arch/x86/mm/pat/memtype.c | 3 +--
>>   1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c
>> index fb4b1b5e0dea..46de9cf5c91d 100644
>> --- a/arch/x86/mm/pat/memtype.c
>> +++ b/arch/x86/mm/pat/memtype.c
>> @@ -387,8 +387,7 @@ static unsigned long pat_x_mtrr_type(u64 start, u64 end,
>>   		u8 mtrr_type, uniform;
>>   
>>   		mtrr_type = mtrr_type_lookup(start, end, &uniform);
>> -		if (mtrr_type != MTRR_TYPE_WRBACK &&
>> -		    mtrr_type != MTRR_TYPE_INVALID)
>> +		if (mtrr_type != MTRR_TYPE_WRBACK)
>>   			return _PAGE_CACHE_MODE_UC_MINUS;
>>   
>>   		return _PAGE_CACHE_MODE_WB;


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