This is a note to let you know that I've just added the patch titled
xen/p2m: Reserve 8MB of _brk space for P2M leafs when populating back.
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
xen-p2m-reserve-8mb-of-_brk-space-for-p2m-leafs-when-populating-back.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 5bc6f9888db5739abfa0cae279b4b442e4db8049 Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <[email protected]>
Date: Mon, 30 Jul 2012 10:18:05 -0400
Subject: xen/p2m: Reserve 8MB of _brk space for P2M leafs when populating back.
From: Konrad Rzeszutek Wilk <[email protected]>
commit 5bc6f9888db5739abfa0cae279b4b442e4db8049 upstream.
When we release pages back during bootup:
Freeing 9d-100 pfn range: 99 pages freed
Freeing 9cf36-9d0d2 pfn range: 412 pages freed
Freeing 9f6bd-9f6bf pfn range: 2 pages freed
Freeing 9f714-9f7bf pfn range: 171 pages freed
Freeing 9f7e0-9f7ff pfn range: 31 pages freed
Freeing 9f800-100000 pfn range: 395264 pages freed
Released 395979 pages of unused memory
We then try to populate those pages back. In the P2M tree however
the space for those leafs must be reserved - as such we use extend_brk.
We reserve 8MB of _brk space, which means we can fit over
1048576 PFNs - which is more than we should ever need.
Without this, on certain compilation of the kernel we would hit:
(XEN) domain_crash_sync called from entry.S
(XEN) CPU: 0
(XEN) RIP: e033:[<ffffffff818aad3b>]
(XEN) RFLAGS: 0000000000000206 EM: 1 CONTEXT: pv guest
(XEN) rax: ffffffff81a7c000 rbx: 000000000000003d rcx: 0000000000001000
(XEN) rdx: ffffffff81a7b000 rsi: 0000000000001000 rdi: 0000000000001000
(XEN) rbp: ffffffff81801cd8 rsp: ffffffff81801c98 r8: 0000000000100000
(XEN) r9: ffffffff81a7a000 r10: 0000000000000001 r11: 0000000000000003
(XEN) r12: 0000000000000004 r13: 0000000000000004 r14: 000000000000003d
(XEN) r15: 00000000000001e8 cr0: 000000008005003b cr4: 00000000000006f0
(XEN) cr3: 0000000125803000 cr2: 0000000000000000
(XEN) ds: 0000 es: 0000 fs: 0000 gs: 0000 ss: e02b cs: e033
(XEN) Guest stack trace from rsp=ffffffff81801c98:
.. which is extend_brk hitting a BUG_ON.
Interestingly enough, most of the time we are not going to hit this
b/c the _brk space is quite large (v3.5):
ffffffff81a25000 B __brk_base
ffffffff81e43000 B __brk_limit
= ~4MB.
vs earlier kernels (with this back-ported), the space is smaller:
ffffffff81a25000 B __brk_base
ffffffff81a7b000 B __brk_limit
= 344 kBytes.
where we would certainly hit this and hit extend_brk.
Note that git commit c3d93f880197953f86ab90d9da4744e926b38e33
(xen: populate correct number of pages when across mem boundary (v2))
exposed this bug).
[v1: Made it 8MB of _brk space instead of 4MB per Jan's suggestion]
Signed-off-by: Daniel Kiper <[email protected]>
Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
arch/x86/xen/p2m.c | 5 +++++
1 file changed, 5 insertions(+)
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -194,6 +194,11 @@ RESERVE_BRK(p2m_mid_mfn, PAGE_SIZE * (MA
* boundary violation will require three middle nodes. */
RESERVE_BRK(p2m_mid_identity, PAGE_SIZE * 2 * 3);
+/* When we populate back during bootup, the amount of pages can vary. The
+ * max we have is seen is 395979, but that does not mean it can't be more.
+ * But some machines can have 3GB I/O holes even. So lets reserve enough
+ * for 4GB of I/O and E820 holes. */
+RESERVE_BRK(p2m_populated, PMD_SIZE * 4);
static inline unsigned p2m_top_index(unsigned long pfn)
{
BUG_ON(pfn >= MAX_P2M_PFN);
Patches currently in stable-queue which might be from [email protected] are
queue-3.4/xen-p2m-move-code-around-to-allow-for-better-re-usage.patch
queue-3.4/xen-populate-correct-number-of-pages-when-across-mem-boundary-v2.patch
queue-3.4/xen-p2m-collapse-early_alloc_p2m_middle-redundant-checks.patch
queue-3.4/xen-setup-populate-freed-mfns-from-non-ram-e820-entries-and-gaps-to-e820-ram.patch
queue-3.4/xen-p2m-reserve-8mb-of-_brk-space-for-p2m-leafs-when-populating-back.patch
queue-3.4/xen-setup-combine-the-two-hypercall-functions-since-they-are-quite-similar.patch
queue-3.4/xen-p2m-allow-alloc_p2m_middle-to-call-reserve_brk-depending-on-argument.patch
queue-3.4/xen-p2m-an-early-bootup-variant-of-set_phys_to_machine.patch
queue-3.4/xen-balloon-subtract-from-xen_released_pages-the-count-that-is-populated.patch
queue-3.4/xen-setup-update-va-mapping-when-releasing-memory-during-setup.patch
queue-3.4/xen-p2m-reuse-existing-p2m-leafs-if-they-are-filled-with-1-1-pfns-or-invalid.patch
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