Re: [Xen-devel] [RESEND PATCH V3 0/3] x86: Full support of PAT

[Juergen Gross <jgross@xxxxxxxx>]

Ping?

On 10/20/2014 05:59 AM, Juergen Gross wrote:
> Hi x86 maintainers,
>
> any reason you seem to ignore this patch series? I think I've replied
> to all open issues and sent the patches more than one month ago. Each
> patch has a "Reviewed-by". Is there something else missing?
>
>
> Juergen
>
> On 10/13/2014 10:13 AM, Juergen Gross wrote:
> > 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
> >
> > Changes in V3:
> > - corrected two minor nits (UC_MINUS, again) detected by Toshi Kani
> >
> > Changes in V2:
> > - simplified handling of PAT MSR write under Xen as suggested by David
> > Vrabel
> > - removed resetting of pat_enabled under Xen
> > - two small corrections requested by Toshi Kani (UC_MINUS cache mode in
> >    vermilion driver, fix 32 bit kernel build failure)
> > - correct build error on non-x86 arch by moving definition of
> >    update_cache_mode_entry() to x86 specific header
> >
> > Changes since RFC:
> > - renamed functions and variables as suggested by Toshi Kani
> > - corrected cache mode bits for WT and WP
> > - modified handling of PAT MSR write under Xen as suggested by Jan
> > Beulich
> >
> >
> > Juergen Gross (3):
> >    x86: Make page cache mode a real type
> >    x86: Enable PAT to use cache mode translation tables
> >    Support Xen pv-domains using PAT
> >
> >   arch/x86/include/asm/cacheflush.h         |  38 ++++---
> >   arch/x86/include/asm/fb.h                 |   6 +-
> >   arch/x86/include/asm/io.h                 |   2 +-
> >   arch/x86/include/asm/pat.h                |   7 +-
> >   arch/x86/include/asm/pgtable.h            |  19 ++--
> >   arch/x86/include/asm/pgtable_types.h      |  96 ++++++++++++----
> >   arch/x86/mm/dump_pagetables.c             |  24 ++--
> >   arch/x86/mm/init.c                        |  37 ++++++
> >   arch/x86/mm/init_64.c                     |   9 +-
> >   arch/x86/mm/iomap_32.c                    |  15 ++-
> >   arch/x86/mm/ioremap.c                     |  63 ++++++-----
> >   arch/x86/mm/mm_internal.h                 |   2 +
> >   arch/x86/mm/pageattr.c                    |  84 ++++++++------
> >   arch/x86/mm/pat.c                         | 181
> > +++++++++++++++++++-----------
> >   arch/x86/mm/pat_internal.h                |  22 ++--
> >   arch/x86/mm/pat_rbtree.c                  |   8 +-
> >   arch/x86/pci/i386.c                       |   4 +-
> >   arch/x86/xen/enlighten.c                  |  25 ++---
> >   arch/x86/xen/mmu.c                        |  48 +-------
> >   arch/x86/xen/xen-ops.h                    |   1 -
> >   drivers/video/fbdev/gbefb.c               |   3 +-
> >   drivers/video/fbdev/vermilion/vermilion.c |   6 +-
> >   22 files changed, 421 insertions(+), 279 deletions(-)
> --
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