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authorKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2012-07-30 10:18:05 -0400
committerKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2012-08-02 10:39:53 -0400
commit5bc6f9888db5739abfa0cae279b4b442e4db8049 (patch)
parentc3d93f880197953f86ab90d9da4744e926b38e33 (diff)
xen/p2m: Reserve 8MB of _brk space for P2M leafs when populating back.
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] CC: stable@vger.kernel.org #only for 3.5 Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 64effdc6da94..b2e91d40a4cb 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -194,6 +194,11 @@ RESERVE_BRK(p2m_mid_mfn, PAGE_SIZE * (MAX_DOMAIN_PAGES / (P2M_PER_PAGE * P2M_MID
* 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);