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a023748d53
Pull x86 mm tree changes from Ingo Molnar:
"The biggest change is full PAT support from Jürgen Gross:
The x86 architecture offers via the PAT (Page Attribute Table) a
way to specify different caching modes in page table entries. The
PAT MSR contains 8 entries each specifying one of 6 possible cache
modes. A pte references one of those entries via 3 bits:
_PAGE_PAT, _PAGE_PWT and _PAGE_PCD.
The Linux kernel currently supports only 4 different cache modes.
The PAT MSR is set up in a way that the setting of _PAGE_PAT in a
pte doesn't matter: the top 4 entries in the PAT MSR are the same
as the 4 lower entries.
This results in the kernel not supporting e.g. write-through mode.
Especially this cache mode would speed up drivers of video cards
which now have to use uncached accesses.
OTOH some old processors (Pentium) don't support PAT correctly and
the Xen hypervisor has been using a different PAT MSR configuration
for some time now and can't change that as this setting is part of
the ABI.
This patch set abstracts the cache mode from the pte and introduces
tables to translate between cache mode and pte bits (the default
cache mode "write back" is hard-wired to PAT entry 0). The tables
are statically initialized with values being compatible to old
processors and current usage. As soon as the PAT MSR is changed
(or - in case of Xen - is read at boot time) the tables are changed
accordingly. Requests of mappings with special cache modes are
always possible now, in case they are not supported there will be a
fallback to a compatible but slower mode.
Summing it up, this patch set adds the following features:
- capability to support WT and WP cache modes on processors with
full PAT support
- processors with no or uncorrect PAT support are still working as
today, even if WT or WP cache mode are selected by drivers for
some pages
- reduction of Xen special handling regarding cache mode
Another change is a boot speedup on ridiculously large RAM systems,
plus other smaller fixes"
* 'x86-mm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (22 commits)
x86: mm: Move PAT only functions to mm/pat.c
xen: Support Xen pv-domains using PAT
x86: Enable PAT to use cache mode translation tables
x86: Respect PAT bit when copying pte values between large and normal pages
x86: Support PAT bit in pagetable dump for lower levels
x86: Clean up pgtable_types.h
x86: Use new cache mode type in memtype related functions
x86: Use new cache mode type in mm/ioremap.c
x86: Use new cache mode type in setting page attributes
x86: Remove looking for setting of _PAGE_PAT_LARGE in pageattr.c
x86: Use new cache mode type in track_pfn_remap() and track_pfn_insert()
x86: Use new cache mode type in mm/iomap_32.c
x86: Use new cache mode type in asm/pgtable.h
x86: Use new cache mode type in arch/x86/mm/init_64.c
x86: Use new cache mode type in arch/x86/pci
x86: Use new cache mode type in drivers/video/fbdev/vermilion
x86: Use new cache mode type in drivers/video/fbdev/gbefb.c
x86: Use new cache mode type in include/asm/fb.h
x86: Make page cache mode a real type
x86: mm: Use 2GB memory block size on large-memory x86-64 systems
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