* Toshi Kani <toshi.k...@hp.com> wrote:
> On Wed, 2015-05-20 at 13:55 +0200, Ingo Molnar wrote:
> > * Borislav Petkov <b...@alien8.de> wrote:
> >
> > > --- a/arch/x86/mm/pgtable.c
> > > +++ b/arch/x86/mm/pgtable.c
> > > @@ -566,19 +566,28 @@ void native_set_fixmap(enum fixed_addresses idx,
> > > phys_addr_t phys,
> > > /**
> > > * pud_set_huge - setup kernel PUD mapping
> > > *
> > > - * MTRR can override PAT memory types with 4KiB granularity. Therefore,
> > > - * this function does not set up a huge page when the range is covered
> > > - * by a non-WB type of MTRR. MTRR_TYPE_INVALID indicates that MTRR are
> > > - * disabled.
> > > + * MTRRs can override PAT memory types with 4KiB granularity. Therefore,
> > > this
> > > + * function sets up a huge page only if any of the following conditions
> > > are met:
> > > + *
> > > + * - MTRRs are disabled, or
> > > + *
> > > + * - MTRRs are enabled and the range is completely covered by a single
> > > MTRR, or
> > > + *
> > > + * - MTRRs are enabled and the range is not completely covered by a
> > > single MTRR
> > > + * but the memory type of the range is WB, even if covered by multiple
> > > MTRRs.
> > > + *
> > > + * Callers should try to decrease page size (1GB -> 2MB -> 4K) if the
> > > bigger
> > > + * page mapping attempt fails.
> >
> > This comment should explain why it's ok in the WB case.
> >
> > Also, the phrase 'the memory type of the range' is ambiguous: it might
> > mean the partial MTRR's, or the memory type specified via PAT by the
> > huge-pmd entry.
>
> Agreed. How about this sentence?
>
> - MTRRs are enabled and the corresponding MTRR memory type is WB, which
> has no effect to the requested PAT memory type.
s/effect to/effect on
sounds good otherwise!
Btw., if WB MTRR entries can never have an effect on Linux PAT
specified attributes, why do we allow them to be created? I don't
think we ever call into real mode for this to matter?
Thanks,
Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
