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    SubjectRe: [tip:x86/urgent] VM, x86, PAT: Change is_linear_pfn_mapping to not use vm_pgoff
    On Fri, Mar 13, 2009 at 04:03:39AM +0000, Pallipadi, Venkatesh wrote:
    > Commit-ID: 4bb9c5c02153dfc89a6c73a6f32091413805ad7d
    > Gitweb: http://git.kernel.org/tip/4bb9c5c02153dfc89a6c73a6f32091413805ad7d
    > Author: Pallipadi, Venkatesh <venkatesh.pallipadi@intel.com>
    > AuthorDate: Thu, 12 Mar 2009 17:45:27 -0700
    > Commit: Ingo Molnar <mingo@elte.hu>
    > CommitDate: Fri, 13 Mar 2009 04:28:50 +0100
    >
    > VM, x86, PAT: Change is_linear_pfn_mapping to not use vm_pgoff
    >
    > Impact: fix false positive PAT warnings - also fix VirtalBox hang
    >
    > Use of vma->vm_pgoff to identify the pfnmaps that are fully
    > mapped at mmap time is broken. vm_pgoff is set by generic mmap
    > code even for cases where drivers are setting up the mappings
    > at the fault time.
    >
    > The problem was originally reported here:
    >
    > http://marc.info/?l=linux-kernel&m=123383810628583&w=2
    >
    > Change is_linear_pfn_mapping logic to overload VM_INSERTPAGE
    > flag along with VM_PFNMAP to mean full PFNMAP setup at mmap
    > time.
    >
    > Problem also tracked at:
    >
    > http://bugzilla.kernel.org/show_bug.cgi?id=12800
    >
    > Reported-by: Thomas Hellstrom <thellstrom@vmware.com>
    > Tested-by: Frans Pop <elendil@planet.nl>
    > Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
    > Signed-off-by: Suresh Siddha <suresh.b.siddha>@intel.com>
    > Cc: Nick Piggin <npiggin@suse.de>
    > Cc: "ebiederm@xmission.com" <ebiederm@xmission.com>
    > Cc: <stable@kernel.org> # only for 2.6.29.1, not .28
    > LKML-Reference: <20090313004527.GA7176@linux-os.sc.intel.com>
    > Signed-off-by: Ingo Molnar <mingo@elte.hu>
    >
    >
    > ---
    > arch/x86/mm/pat.c | 5 +++--
    > include/linux/mm.h | 15 +++++++++++++--
    > mm/memory.c | 6 ++++--
    > 3 files changed, 20 insertions(+), 6 deletions(-)
    >
    > diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
    > index e0ab173..21bc1f7 100644
    > --- a/arch/x86/mm/pat.c
    > +++ b/arch/x86/mm/pat.c
    > @@ -641,10 +641,11 @@ static int reserve_pfn_range(u64 paddr, unsigned long size, pgprot_t *vma_prot,
    > is_ram = pat_pagerange_is_ram(paddr, paddr + size);
    >
    > /*
    > - * reserve_pfn_range() doesn't support RAM pages.
    > + * reserve_pfn_range() doesn't support RAM pages. Maintain the current
    > + * behavior with RAM pages by returning success.
    > */
    > if (is_ram != 0)
    > - return -EINVAL;
    > + return 0;
    >
    > ret = reserve_memtype(paddr, paddr + size, want_flags, &flags);
    > if (ret)
    > diff --git a/include/linux/mm.h b/include/linux/mm.h
    > index 065cdf8..3daa05f 100644
    > --- a/include/linux/mm.h
    > +++ b/include/linux/mm.h
    > @@ -98,7 +98,7 @@ extern unsigned int kobjsize(const void *objp);
    > #define VM_HUGETLB 0x00400000 /* Huge TLB Page VM */
    > #define VM_NONLINEAR 0x00800000 /* Is non-linear (remap_file_pages) */
    > #define VM_MAPPED_COPY 0x01000000 /* T if mapped copy of data (nommu mmap) */
    > -#define VM_INSERTPAGE 0x02000000 /* The vma has had "vm_insert_page()" done on it */
    > +#define VM_INSERTPAGE 0x02000000 /* The vma has had "vm_insert_page()" done on it. Refer note in VM_PFNMAP_AT_MMAP below */
    > #define VM_ALWAYSDUMP 0x04000000 /* Always include in core dumps */
    >
    > #define VM_CAN_NONLINEAR 0x08000000 /* Has ->fault & does nonlinear pages */
    > @@ -127,6 +127,17 @@ extern unsigned int kobjsize(const void *objp);
    > #define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_RESERVED | VM_PFNMAP)
    >
    > /*
    > + * pfnmap vmas that are fully mapped at mmap time (not mapped on fault).
    > + * Used by x86 PAT to identify such PFNMAP mappings and optimize their handling.
    > + * Note VM_INSERTPAGE flag is overloaded here. i.e,
    > + * VM_INSERTPAGE && !VM_PFNMAP implies
    > + * The vma has had "vm_insert_page()" done on it
    > + * VM_INSERTPAGE && VM_PFNMAP implies
    > + * The vma is PFNMAP with full mapping at mmap time
    > + */
    > +#define VM_PFNMAP_AT_MMAP (VM_INSERTPAGE | VM_PFNMAP)

    This is really ugly IMO. Either it should be its own bit, or if you want
    to reduce usage of bits, then set aside some bits to represent a set of
    vma types, and convert existing code over to use that.

    Why not just use another vm_flag for 2.6.29 and earlier (we have 2 left),
    then do some flag rationalisation in 2.6.30?

    But I do like just avoiding these games entirely and encoding it
    explicitly.


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