Messages in this thread | | | Date | Wed, 20 May 2015 13:55:09 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH v5 6/6] mtrr, mm, x86: Enhance MTRR checks for KVA huge page mapping |
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* Borislav Petkov <bp@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.
Thanks,
Ingo
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