linux-kernel - Re: [tip: x86/urgent] x86/mtrr: Revert 90b926e68f50 ("x86/pat: Fix pat_x_mtrr

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Date:   Sat, 18 Feb 2023 10:47:46 +0100 (CET)
From:   Christian Kujau <lists@...dbynature.de>
To:     linux-kernel@...r.kernel.org
cc:     Juergen Gross <jgross@...e.com>,
        "Borislav Petkov (AMD)" <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [tip: x86/urgent] x86/mtrr: Revert 90b926e68f50 ("x86/pat: Fix
 pat_x_mtrr_type() for MTRR disabled case")

On Tue, 14 Feb 2023, tip-bot2 for Juergen Gross wrote:
> The following commit has been merged into the x86/urgent branch of tip:

Sorry for being dense but I couldn't figure this out from the tip tree 
handbook[0]: will this be included in 6.2 or has this ship sailed? If so, 
I'll start bugging the Alpine folks to maybe carry this around until the 
next release.

Thanks,
Christian.

[0] https://www.kernel.org/doc/html/latest/process/maintainer-tip.html

> 
> Commit-ID:     f9f57da2c2d119dbf109e3f6e1ceab7659294046
> Gitweb:        https://git.kernel.org/tip/f9f57da2c2d119dbf109e3f6e1ceab7659294046
> Author:        Juergen Gross <jgross@...e.com>
> AuthorDate:    Thu, 09 Feb 2023 08:22:17 +01:00
> Committer:     Borislav Petkov (AMD) <bp@...en8.de>
> CommitterDate: Tue, 14 Feb 2023 10:16:34 +01:00
> 
> x86/mtrr: Revert 90b926e68f50 ("x86/pat: Fix pat_x_mtrr_type() for MTRR disabled case")
> 
> Commit
> 
>   90b926e68f50 ("x86/pat: Fix pat_x_mtrr_type() for MTRR disabled case")
> 
> broke the use case of running Xen dom0 kernels on machines with an
> external disk enclosure attached via USB, see Link tag.
> 
> What this commit was originally fixing - SEV-SNP guests on Hyper-V - is
> a more specialized situation which has other issues at the moment anyway
> so reverting this now and addressing the issue properly later is the
> prudent thing to do.
> 
> So revert it in time for the 6.2 proper release.
> 
>   [ bp: Rewrite commit message. ]
> 
> Reported-by: Christian Kujau <lists@...dbynature.de>
> Tested-by: Christian Kujau <lists@...dbynature.de>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
> Link: https://lore.kernel.org/r/4fe9541e-4d4c-2b2a-f8c8-2d34a7284930@nerdbynature.de
> ---
>  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 fb4b1b5..46de9cf 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;
> 

-- 
BOFH excuse #155:

Dumb terminal