On Wed, 2015-05-20 at 13:55 +0200, Ingo Molnar wrote: > * Borislav Petkov <bp@xxxxxxxxx> 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. Thanks, -Toshi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>