xen: properly account for _PAGE_NUMA during xen pte translations

Steven Noonan forwarded a users report where they had a problem starting
vsftpd on a Xen paravirtualized guest, with this in dmesg:

  BUG: Bad page map in process vsftpd  pte:8000000493b88165 pmd:e9cc01067
  page:ffffea00124ee200 count:0 mapcount:-1 mapping:     (null) index:0x0
  page flags: 0x2ffc0000000014(referenced|dirty)
  addr:00007f97eea74000 vm_flags:00100071 anon_vma:ffff880e98f80380 mapping:          (null) index:7f97eea74
  CPU: 4 PID: 587 Comm: vsftpd Not tainted 3.12.7-1-ec2 #1
  Call Trace:
    dump_stack+0x45/0x56
    print_bad_pte+0x22e/0x250
    unmap_single_vma+0x583/0x890
    unmap_vmas+0x65/0x90
    exit_mmap+0xc5/0x170
    mmput+0x65/0x100
    do_exit+0x393/0x9e0
    do_group_exit+0xcc/0x140
    SyS_exit_group+0x14/0x20
    system_call_fastpath+0x1a/0x1f
  Disabling lock debugging due to kernel taint
  BUG: Bad rss-counter state mm:ffff880e9ca60580 idx:0 val:-1
  BUG: Bad rss-counter state mm:ffff880e9ca60580 idx:1 val:1

The issue could not be reproduced under an HVM instance with the same
kernel, so it appears to be exclusive to paravirtual Xen guests.  He
bisected the problem to commit 1667918b6483 ("mm: numa: clear numa
hinting information on mprotect") that was also included in 3.12-stable.

The problem was related to how xen translates ptes because it was not
accounting for the _PAGE_NUMA bit.  This patch splits pte_present to add
a pteval_present helper for use by xen so both bare metal and xen use
the same code when checking if a PTE is present.

[mgorman@suse.de: wrote changelog, proposed minor modifications]
[akpm@linux-foundation.org: fix typo in comment]
Reported-by: Steven Noonan <steven@uplinklabs.net>
Tested-by: Steven Noonan <steven@uplinklabs.net>
Signed-off-by: Elena Ufimtseva <ufimtseva@gmail.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: <stable@vger.kernel.org>	[3.12+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index bbc8b12fa443d47ee9a8faa59b36767e7aec866c..5ad38ad07890fc4ca8698aae41c6e60e48a451f4 100644 (file)
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -445,10 +445,20 @@ static inline int pte_same(pte_t a, pte_t b)
        return a.pte == b.pte;
 }
 
+static inline int pteval_present(pteval_t pteval)
+{
+       /*
+        * Yes Linus, _PAGE_PROTNONE == _PAGE_NUMA. Expressing it this
+        * way clearly states that the intent is that protnone and numa
+        * hinting ptes are considered present for the purposes of
+        * pagetable operations like zapping, protection changes, gup etc.
+        */
+       return pteval & (_PAGE_PRESENT | _PAGE_PROTNONE | _PAGE_NUMA);
+}
+
 static inline int pte_present(pte_t a)
 {
-       return pte_flags(a) & (_PAGE_PRESENT | _PAGE_PROTNONE |
-                              _PAGE_NUMA);
+       return pteval_present(pte_flags(a));
 }
 
 #define pte_accessible pte_accessible

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 2423ef04ffea596fd43eeb918f290003277fbb21..256282e7888b118b02e61d657f78ae8490bf0fe4 100644 (file)
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -365,7 +365,7 @@ void xen_ptep_modify_prot_commit(struct mm_struct *mm, unsigned long addr,
 /* Assume pteval_t is equivalent to all the other *val_t types. */
 static pteval_t pte_mfn_to_pfn(pteval_t val)
 {
-       if (val & _PAGE_PRESENT) {
+       if (pteval_present(val)) {
                unsigned long mfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
                unsigned long pfn = mfn_to_pfn(mfn);
 
@@ -381,7 +381,7 @@ static pteval_t pte_mfn_to_pfn(pteval_t val)
 
 static pteval_t pte_pfn_to_mfn(pteval_t val)
 {
-       if (val & _PAGE_PRESENT) {
+       if (pteval_present(val)) {
                unsigned long pfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
                pteval_t flags = val & PTE_FLAGS_MASK;
                unsigned long mfn;