xen: properly account for _PAGE_NUMA during xen pte translations

Mel Gorman · torvalds · commit a9c8e4beeeb6 · 2014-02-10T16:01:41.000-08:00
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 1667918 ("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
@@ -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
@@ -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;
