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

[Juergen Gross]

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@xxxxxxxxxxxxxxx/
>
> P.S.: BTW; let me tell regzbot to monitor this thread:
>
> #regzbot ^backmonitor:
> https://lore.kernel.org/all/4fe9541e-4d4c-2b2a-f8c8-2d34a7284930@xxxxxxxxxxxxxxx/
>
>
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> >   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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