Re: [PATCH] x86/mm: fix regression with huge pages on PAE

[Boris Ostrovsky]

On 11/12/2015 04:00 AM, Kirill A. Shutemov wrote:
> On Thu, Nov 12, 2015 at 09:54:18AM +0100, Ingo Molnar wrote:
> > * Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> >
> > > diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h
> > > index c5b7fb2774d0..cc071c6f7d4d 100644
> > > --- a/arch/x86/include/asm/page_types.h
> > > +++ b/arch/x86/include/asm/page_types.h


Kirill, where are we with this patch?

-boris

> > > @@ -9,19 +9,21 @@
> > >   #define PAGE_SIZE	(_AC(1,UL) << PAGE_SHIFT)
> > >   #define PAGE_MASK	(~(PAGE_SIZE-1))
> > >   
> > > +#define PMD_PAGE_SIZE		(_AC(1, UL) << PMD_SHIFT)
> > > +#define PMD_PAGE_MASK		(~(PMD_PAGE_SIZE-1))
> > > +
> > > +#define PUD_PAGE_SIZE		(_AC(1, UL) << PUD_SHIFT)
> > > +#define PUD_PAGE_MASK		(~(PUD_PAGE_SIZE-1))
> > > +
> > >   #define __PHYSICAL_MASK		((phys_addr_t)((1ULL << __PHYSICAL_MASK_SHIFT) - 1))
> > >   #define __VIRTUAL_MASK		((1UL << __VIRTUAL_MASK_SHIFT) - 1)
> > >   
> > > -/* Cast PAGE_MASK to a signed type so that it is sign-extended if
> > > +/* Cast *PAGE_MASK to a signed type so that it is sign-extended if
> > >      virtual addresses are 32-bits but physical addresses are larger
> > >      (ie, 32-bit PAE). */
> > >   #define PHYSICAL_PAGE_MASK	(((signed long)PAGE_MASK) & __PHYSICAL_MASK)
> > > -
> > > -#define PMD_PAGE_SIZE		(_AC(1, UL) << PMD_SHIFT)
> > > -#define PMD_PAGE_MASK		(~(PMD_PAGE_SIZE-1))
> > > -
> > > -#define PUD_PAGE_SIZE		(_AC(1, UL) << PUD_SHIFT)
> > > -#define PUD_PAGE_MASK		(~(PUD_PAGE_SIZE-1))
> > > +#define PHYSICAL_PMD_PAGE_MASK	(((signed long)PMD_PAGE_MASK) & __PHYSICAL_MASK)
> > > +#define PHYSICAL_PUD_PAGE_MASK	(((signed long)PUD_PAGE_MASK) & __PHYSICAL_MASK)
> > that's a really odd way of writing it, 'long' is signed by default ...
> See the comment above (it was there before the patch). 'signed' can be
> considered as documentation -- we want sign-extension here.
>
> > There seems to be 150+ such cases in the kernel source though - weird.
> >
> > More importantly, how does this improve things on 32-bit PAE kernels? If I follow
> > the values correctly then PMD_PAGE_MASK is 'UL' i.e. 32-bit:
> >
> > > +#define PMD_PAGE_SIZE                (_AC(1, UL) << PMD_SHIFT)
> > > +#define PMD_PAGE_MASK                (~(PMD_PAGE_SIZE-1))
> > thus PHYSICAL_PMD_PAGE_MASK is 32-bit too:
> >
> > > +#define PHYSICAL_PMD_PAGE_MASK       (((signed long)PMD_PAGE_MASK) & __PHYSICAL_MASK)
> > so how is the bug fixed?
> Again, see the comment.
> I've checked that it generates correct value (using kernel/bounds.c).

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