From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: [PATCH V3 0/3] x86: Full support of PAT Date: Tue, 23 Sep 2014 07:31:20 +0200 Message-ID: <542105A8.3060004@suse.com> References: <1410518112-2625-1-git-send-email-jgross@suse.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1410518112-2625-1-git-send-email-jgross@suse.com> Sender: linux-kernel-owner@vger.kernel.org To: stefan.bader@canonical.com, toshi.kani@hp.com, linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com, konrad.wilk@oracle.com, ville.syrjala@linux.intel.com, hpa@zytor.com, x86@kernel.org, david.vrabel@citrix.com, jbeulich@suse.com, mingo@redhat.com, tglx@linutronix.de List-Id: xen-devel@lists.xenproject.org Hi, any chance to have this in 3.18? Juergen On 09/12/2014 12:35 PM, 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(-) >