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

[Kirill A. Shutemov]

Ingo Molnar wrote:
> 
> * Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote:
> 
> > On Thu, Nov 12, 2015 at 08:48:54AM +0100, Ingo Molnar wrote:
> > > 
> > > * Borislav Petkov <bp@xxxxxxxxx> wrote:
> > > 
> > > > --- a/arch/x86/include/asm/pgtable_types.h
> > > > +++ b/arch/x86/include/asm/pgtable_types.h
> > > > @@ -279,17 +279,14 @@ static inline pmdval_t native_pmd_val(pmd_t pmd)
> > > >  static inline pudval_t pud_pfn_mask(pud_t pud)
> > > >  {
> > > >  	if (native_pud_val(pud) & _PAGE_PSE)
> > > > -		return PUD_PAGE_MASK & PHYSICAL_PAGE_MASK;
> > > > +		return ~((1ULL << PUD_SHIFT) - 1) & PHYSICAL_PAGE_MASK;
> > > >  	else
> > > >  		return PTE_PFN_MASK;
> > > >  }
> > > 
> > > >  static inline pmdval_t pmd_pfn_mask(pmd_t pmd)
> > > >  {
> > > >  	if (native_pmd_val(pmd) & _PAGE_PSE)
> > > > -		return PMD_PAGE_MASK & PHYSICAL_PAGE_MASK;
> > > > +		return ~((1ULL << PMD_SHIFT) - 1) & PHYSICAL_PAGE_MASK;
> > > >  	else
> > > >  		return PTE_PFN_MASK;
> > > >  }
> > > 
> > > So instead of uglifying the code, why not fix the real bug: change the 
> > > PMD_PAGE_MASK/PUD_PAGE_MASK definitions to be 64-bit everywhere?
> > 
> > *PAGE_MASK are usually applied to virtual addresses. I don't think it
> > should anything but 'unsigned long'. This is odd use case really.
> 
> So we already have PHYSICAL_PAGE_MASK, why not introduce PHYSICAL_PMD_MASK et al, 
> instead of uglifying the code?

Okay, makes sense. Check out the patch below.

> But, what problems do you expect with having a wider mask than its primary usage? 
> If it's used for 32-bit values it will be truncated down safely. (But I have not 
> tested it, so I might be missing some complication.)

Yeah, I basically worry about non realized side effect.

And these masks are defined via {PMD,PUD}_PAGE_SIZE. Should we change them
to 'unsigned long long' too or leave alone? What about PAGE_SIZE and
PAGE_MASK? Need to be converted too?