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Subject[tip:x86/mm] x86, mm: Hold mm->page_table_lock while doing vmalloc_sync
Commit-ID:  617d34d9e5d8326ec8f188c616aa06ac59d083fe
Gitweb: http://git.kernel.org/tip/617d34d9e5d8326ec8f188c616aa06ac59d083fe
Author: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
AuthorDate: Tue, 21 Sep 2010 12:01:51 -0700
Committer: H. Peter Anvin <hpa@linux.intel.com>
CommitDate: Tue, 19 Oct 2010 13:57:08 -0700

x86, mm: Hold mm->page_table_lock while doing vmalloc_sync

Take mm->page_table_lock while syncing the vmalloc region. This prevents
a race with the Xen pagetable pin/unpin code, which expects that the
page_table_lock is already held. If this race occurs, then Xen can see
an inconsistent page type (a page can either be read/write or a pagetable
page, and pin/unpin converts it between them), which will cause either
the pin or the set_p[gm]d to fail; either will crash the kernel.

vmalloc_sync_all() should be called rarely, so this extra use of
page_table_lock should not interfere with its normal users.

The mm pointer is stashed in the pgd page's index field, as that won't
be otherwise used for pgds.

Reported-by: Ian Campbell <ian.cambell@eu.citrix.com>
Originally-by: Jan Beulich <jbeulich@novell.com>
LKML-Reference: <4CB88A4C.1080305@goop.org>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
---
arch/x86/include/asm/pgtable.h | 2 ++
arch/x86/mm/fault.c | 11 ++++++++++-
arch/x86/mm/init_64.c | 7 +++++++
arch/x86/mm/pgtable.c | 20 +++++++++++++++++---
4 files changed, 36 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 2d0a33b..ada823a 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -28,6 +28,8 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
extern spinlock_t pgd_lock;
extern struct list_head pgd_list;

+extern struct mm_struct *pgd_page_get_mm(struct page *page);
+
#ifdef CONFIG_PARAVIRT
#include <asm/paravirt.h>
#else /* !CONFIG_PARAVIRT */
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index caec229..6c27c39 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -229,7 +229,16 @@ void vmalloc_sync_all(void)

spin_lock_irqsave(&pgd_lock, flags);
list_for_each_entry(page, &pgd_list, lru) {
- if (!vmalloc_sync_one(page_address(page), address))
+ spinlock_t *pgt_lock;
+ int ret;
+
+ pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
+
+ spin_lock(pgt_lock);
+ ret = vmalloc_sync_one(page_address(page), address);
+ spin_unlock(pgt_lock);
+
+ if (!ret)
break;
}
spin_unlock_irqrestore(&pgd_lock, flags);
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 1ad7c0f..4d323fb 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -116,12 +116,19 @@ void sync_global_pgds(unsigned long start, unsigned long end)
spin_lock_irqsave(&pgd_lock, flags);
list_for_each_entry(page, &pgd_list, lru) {
pgd_t *pgd;
+ spinlock_t *pgt_lock;
+
pgd = (pgd_t *)page_address(page) + pgd_index(address);
+ pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
+ spin_lock(pgt_lock);
+
if (pgd_none(*pgd))
set_pgd(pgd, *pgd_ref);
else
BUG_ON(pgd_page_vaddr(*pgd)
!= pgd_page_vaddr(*pgd_ref));
+
+ spin_unlock(pgt_lock);
}
spin_unlock_irqrestore(&pgd_lock, flags);
}
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 5c4ee42..c70e57d 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -87,7 +87,19 @@ static inline void pgd_list_del(pgd_t *pgd)
#define UNSHARED_PTRS_PER_PGD \
(SHARED_KERNEL_PMD ? KERNEL_PGD_BOUNDARY : PTRS_PER_PGD)

-static void pgd_ctor(pgd_t *pgd)
+
+static void pgd_set_mm(pgd_t *pgd, struct mm_struct *mm)
+{
+ BUILD_BUG_ON(sizeof(virt_to_page(pgd)->index) < sizeof(mm));
+ virt_to_page(pgd)->index = (pgoff_t)mm;
+}
+
+struct mm_struct *pgd_page_get_mm(struct page *page)
+{
+ return (struct mm_struct *)page->index;
+}
+
+static void pgd_ctor(struct mm_struct *mm, pgd_t *pgd)
{
/* If the pgd points to a shared pagetable level (either the
ptes in non-PAE, or shared PMD in PAE), then just copy the
@@ -105,8 +117,10 @@ static void pgd_ctor(pgd_t *pgd)
}

/* list required to sync kernel mapping updates */
- if (!SHARED_KERNEL_PMD)
+ if (!SHARED_KERNEL_PMD) {
+ pgd_set_mm(pgd, mm);
pgd_list_add(pgd);
+ }
}

static void pgd_dtor(pgd_t *pgd)
@@ -272,7 +286,7 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
*/
spin_lock_irqsave(&pgd_lock, flags);

- pgd_ctor(pgd);
+ pgd_ctor(mm, pgd);
pgd_prepopulate_pmd(mm, pgd, pmds);

spin_unlock_irqrestore(&pgd_lock, flags);

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