Linux Archive

Linux Archive (http://www.linux-archive.org/)
-   Ubuntu Kernel Team (http://www.linux-archive.org/ubuntu-kernel-team/)
-   -   x86/paravirt: PTE updates in k(un)map_atomic need to be synchronous, regardless of lazy_mmu mode (http://www.linux-archive.org/ubuntu-kernel-team/605143-x86-paravirt-pte-updates-k-un-map_atomic-need-synchronous-regardless-lazy_mmu-mode.html)

Konrad Rzeszutek Wilk 11-30-2011 03:03 AM

x86/paravirt: PTE updates in k(un)map_atomic need to be synchronous, regardless of lazy_mmu mode
 
Fix an outstanding issue that has been reported since 2.6.37. Under a
heavy loaded machine processing "fork()" calls could crash with:

BUG: unable to handle kernel paging request at f573fc8c
IP: [<c01abc54>] swap_count_continued+0x104/0x180
*pdpt = 000000002a3b9027 *pde = 0000000001bed067 *pte = 0000000000000000
Oops: 0000 [#1] SMP
Modules linked in:
Pid: 1638, comm: apache2 Not tainted 3.0.4-linode37 #1
EIP: 0061:[<c01abc54>] EFLAGS: 00210246 CPU: 3
EIP is at swap_count_continued+0x104/0x180
.. snip..
Call Trace:
[<c01ac222>] ? __swap_duplicate+0xc2/0x160
[<c01040f7>] ? pte_mfn_to_pfn+0x87/0xe0
[<c01ac2e4>] ? swap_duplicate+0x14/0x40
[<c01a0a6b>] ? copy_pte_range+0x45b/0x500
[<c01a0ca5>] ? copy_page_range+0x195/0x200
[<c01328c6>] ? dup_mmap+0x1c6/0x2c0
[<c0132cf8>] ? dup_mm+0xa8/0x130
[<c013376a>] ? copy_process+0x98a/0xb30
[<c013395f>] ? do_fork+0x4f/0x280
[<c01573b3>] ? getnstimeofday+0x43/0x100
[<c010f770>] ? sys_clone+0x30/0x40
[<c06c048d>] ? ptregs_clone+0x15/0x48
[<c06bfb71>] ? syscall_call+0x7/0xb

The problem is that in copy_page_range() we turn lazy mode on, and then in
swap_entry_free() we call swap_count_continued() which ends up in:

map = kmap_atomic(page, KM_USER0) + offset;

and then later we touch *map.

Since we are running in batched mode (lazy) we don't actually set up the
PTE mappings and the kmap_atomic is not done synchronously and ends up
trying to dereference a page that has not been set.

Looking at kmap_atomic_prot_pfn(), it uses 'arch_flush_lazy_mmu_mode' and
doing the same in kmap_atomic_prot() and __kunmap_atomic() makes the problem
go away.

Interestingly, commit b8bcfe997e4615 ("x86/paravirt: remove lazy mode in
interrupts") removed part of this to fix an interrupt issue - but it went
to far and did not consider this scenario.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

BugLink: http://bugs.launchpad.net/bugs/854050
(cherry-picked from b39e4363068122a5d36a26cc656c365d2341c1d8 linux-next)
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
---
arch/x86/mm/highmem_32.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/arch/x86/mm/highmem_32.c b/arch/x86/mm/highmem_32.c
index b499626..f4f29b1 100644
--- a/arch/x86/mm/highmem_32.c
+++ b/arch/x86/mm/highmem_32.c
@@ -45,6 +45,7 @@ void *kmap_atomic_prot(struct page *page, pgprot_t prot)
vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
BUG_ON(!pte_none(*(kmap_pte-idx)));
set_pte(kmap_pte-idx, mk_pte(page, prot));
+ arch_flush_lazy_mmu_mode();

return (void *)vaddr;
}
@@ -88,6 +89,7 @@ void __kunmap_atomic(void *kvaddr)
*/
kpte_clear_flush(kmap_pte-idx, vaddr);
kmap_atomic_idx_pop();
+ arch_flush_lazy_mmu_mode();
}
#ifdef CONFIG_DEBUG_HIGHMEM
else {
--
1.7.5.4


--
kernel-team mailing list
kernel-team@lists.ubuntu.com
https://lists.ubuntu.com/mailman/listinfo/kernel-team


All times are GMT. The time now is 08:16 AM.

VBulletin, Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Relevant URLs by vBSEO ©2007, Crawlability, Inc.