Re: [tip: x86/urgent] x86/mtrr: Revert 90b926e68f50 ("x86/pat: Fix pat_x_mtrr_type() for MTRR disabled case")

From: Christian Kujau
Date: Sat Feb 18 2023 - 04:47:55 EST


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@xxxxxxxx>
> AuthorDate: Thu, 09 Feb 2023 08:22:17 +01:00
> Committer: Borislav Petkov (AMD) <bp@xxxxxxxxx>
> 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@xxxxxxxxxxxxxxx>
> Tested-by: Christian Kujau <lists@xxxxxxxxxxxxxxx>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
> Link: https://lore.kernel.org/r/4fe9541e-4d4c-2b2a-f8c8-2d34a7284930@xxxxxxxxxxxxxxx
> ---
> 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