Re: [PATCH] GHES: correct page protection flags in ghes_ioremap_pfn_...()

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On Fri, 2012-09-07 at 08:12 +0100, Jan Beulich wrote:
> >>> On 07.09.12 at 09:02, Huang Ying <ying.huang@xxxxxxxxx> wrote:
> > On Fri, 2012-09-07 at 07:40 +0100, Jan Beulich wrote:
> >> At least for Xen Dom0 it is very relevant to set the _PAGE_IO bit when
> >> ioremap-ing (non-RAM) areas, as that flag suppresses the PFN -> MFN
> >> translation otherwise done in PV guests. (The offending commit was
> >> 81e88fdc432a1552401d6e91a984dcccce72b8dc.)
> > 
> > If my understanding were correct, ghes_ioremap_pfn_nmi normally only map
> > RAM.
> 
> But not RAM in the sense of what is seen as usable memory in the
> E820 map. What you're mapping here is reserved memory, and that
> is (from the perspective of the kernel and Xen) non-RAM. The fact
> that it is RAM from a machine perspective is manifested by the
> mapping not needing to be done UC or alike.

I think the key is to keep these memory range map consistent between
each other.  BIOS may map these memory cached.  ACPI may mapped them as
cached (see acpi_os_ioremap) too.

Best Regards,
Huang Ying



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