Re: [PATCH v5 6/6] mtrr, mm, x86: Enhance MTRR checks for KVA huge page mapping

Borislav Petkov
2015-05-19T11:44:49Z

On Mon, May 18, 2015 at 03:53:14PM -0600, Toshi Kani wrote:
> On Mon, 2015-05-18 at 22:51 +0200, Borislav Petkov wrote:
> > On Mon, May 18, 2015 at 02:21:08PM -0600, Toshi Kani wrote:
> > > The caller is the one who makes the condition checks necessary to create
> > > a huge page mapping.
> >
> > How? It would go and change MTRRs configuration and ranges and their
> > memory types so that a huge mapping succeeds?
> >
> > Or go and try a different range?
>
> Try with a smaller page size.
>
> The callers, pud_set_huge() and pmd_set_huge(), check if the given range
> is safe with MTRRs for creating a huge page mapping. If not, they fail
> the request, which leads their callers, ioremap_pud_range() and
> ioremap_pmd_range(), to retry with a smaller page size, i.e. 1GB -> 2MB
> -> 4KB. 4KB may not have overlap with MTRRs (hence no checking is
> necessary), which will succeed as before.

Ok, now *this* should be in the form of a comment over the KVA helpers,
not the MTRR aspect. Callers of those functions would have to know that
- they shouldn't care about MTRR setup.

The MTRR aspect with the 3 conditions should be only over
mtrr_type_lookup().

I'll integrate it into the patch.

--
Regards/Gruss,
Boris.

ECO tip #101: Trim your mails when you reply.
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