releases/2.6.32.10/x86-xen-disable-highmem-pte-allocation-even-when-config_highpte-y.patch

   1 From 817a824b75b1475f1b067c8cee318c7b4d66fcde Mon Sep 17 00:00:00 2001
   2 From: Ian Campbell <ian.campbell@citrix.com>
   3 Date: Fri, 26 Feb 2010 17:16:00 +0000
   4 Subject: x86, xen: Disable highmem PTE allocation even when CONFIG_HIGHPTE=y
   5 MIME-Version: 1.0
   6 Content-Type: text/plain; charset=UTF-8
   7 Content-Transfer-Encoding: 8bit
   8
   9 From: Ian Campbell <ian.campbell@citrix.com>
  10
  11 commit 817a824b75b1475f1b067c8cee318c7b4d66fcde upstream.
  12
  13 There's a path in the pagefault code where the kernel deliberately
  14 breaks its own locking rules by kmapping a high pte page without
  15 holding the pagetable lock (in at least page_check_address). This
  16 breaks Xen's ability to track the pinned/unpinned state of the
  17 page. There does not appear to be a viable workaround for this
  18 behaviour so simply disable HIGHPTE for all Xen guests.
  19
  20 Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
  21 LKML-Reference: <1267204562-11844-1-git-send-email-ian.campbell@citrix.com>
  22 Cc: Jeremy Fitzhardinge <jeremy@goop.org>
  23 Cc: Ingo Molnar <mingo@elte.hu>
  24 Cc: Pasi Kärkkäinen <pasik@iki.fi>
  25 Cc: <xen-devel@lists.xensource.com>
  26 Signed-off-by: H. Peter Anvin <hpa@zytor.com>
  27 Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
  28
  29 ---
  30  arch/x86/xen/enlighten.c |    7 +++++++
  31  arch/x86/xen/mmu.c       |   11 ++++++-----
  32  2 files changed, 13 insertions(+), 5 deletions(-)
  33
  34 --- a/arch/x86/xen/enlighten.c
  35 +++ b/arch/x86/xen/enlighten.c
  36 @@ -48,6 +48,7 @@
  37  #include <asm/traps.h>
  38  #include <asm/setup.h>
  39  #include <asm/desc.h>
  40 +#include <asm/pgalloc.h>
  41  #include <asm/pgtable.h>
  42  #include <asm/tlbflush.h>
  43  #include <asm/reboot.h>
  44 @@ -1092,6 +1093,12 @@ asmlinkage void __init xen_start_kernel(
  45
  46         __supported_pte_mask |= _PAGE_IOMAP;
  47
  48 +       /*
  49 +        * Prevent page tables from being allocated in highmem, even
  50 +        * if CONFIG_HIGHPTE is enabled.
  51 +        */
  52 +       __userpte_alloc_gfp &= ~__GFP_HIGHMEM;
  53 +
  54  #ifdef CONFIG_X86_64
  55         /* Work out if we support NX */
  56         check_efer();
  57 --- a/arch/x86/xen/mmu.c
  58 +++ b/arch/x86/xen/mmu.c
  59 @@ -1432,14 +1432,15 @@ static void *xen_kmap_atomic_pte(struct
  60  {
  61         pgprot_t prot = PAGE_KERNEL;
  62
  63 +       /*
  64 +        * We disable highmem allocations for page tables so we should never
  65 +        * see any calls to kmap_atomic_pte on a highmem page.
  66 +        */
  67 +       BUG_ON(PageHighMem(page));
  68 +
  69         if (PagePinned(page))
  70                 prot = PAGE_KERNEL_RO;
  71
  72 -       if (0 && PageHighMem(page))
  73 -               printk("mapping highpte %lx type %d prot %s\n",
  74 -                      page_to_pfn(page), type,
  75 -                      (unsigned long)pgprot_val(prot) & _PAGE_RW ? "WRITE" : "READ");
  76 -
  77         return kmap_atomic_prot(page, type, prot);
  78  }
  79  #endif