Re: [RFC PATCH 3/11] x86, mm, pat: Change reserve_memtype() to handle WT type

From: Toshi Kani
Date: Tue Jul 15 2014 - 19:19:50 EST

On Tue, 2014-07-15 at 12:56 -0700, Andy Lutomirski wrote:
> On Tue, Jul 15, 2014 at 12:34 PM, Toshi Kani <toshi.kani@xxxxxx> wrote:
> > This patch changes reserve_memtype() to handle the new WT type.
> > When (!pat_enabled && new_type), it continues to set either WB
> > or UC- to *new_type. When pat_enabled, it can reserve a given
> > non-RAM range for WT. At this point, it may not reserve a RAM
> > range for WT since reserve_ram_pages_type() uses the page flags
> > limited to three memory types, WB, WC and UC.
> FWIW, last time I looked at this, it seemed like all the fancy
> reserve_ram_pages stuff was unnecessary: shouldn't the RAM type be
> easy to track in the direct map page tables?

Are you referring the direct map page tables as the kernel page
directory tables (pgd/pud/..)?

I think it needs to be able to keep track of the memory type per a
physical memory range, not per a translation, in order to prevent
aliasing of the memory type.


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