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Date: Thu, 16 Jul 2015 16:47:17 +0800
From: Baoquan He <bhe@...hat.com>
To: linux-kernel@...r.kernel.org, ncroxon@...hat.com,
dyoung@...hat.com, mhuang@...hat.com
Cc: Baoquan He <bhe@...hat.com>
Subject: [RHEL6.8 Patch 19/19] fs/proc/vmcore.c:mmap_vmcore: skip non-ram pages reported by hypervisors
Resolves: bz1097904
https://bugzilla.redhat.com/show_bug.cgi?id=1097904
This is back ported from upstream.
commit 0692dedcf64bf3cdcfb9f6a51c70d49c8db351d2
Author: Vitaly Kuznetsov <vkuznets@...hat.com>
Date: Fri Aug 8 14:22:05 2014 -0700
fs/proc/vmcore.c:mmap_vmcore: skip non-ram pages reported by hypervisors
We have a special check in read_vmcore() handler to check if the page was
reported as ram or not by the hypervisor (pfn_is_ram()). However, when
vmcore is read with mmap() no such check is performed. That can lead to
unpredictable results, e.g. when running Xen PVHVM guest memcpy() after
mmap() on /proc/vmcore will hang processing HVMMEM_mmio_dm pages creating
enormous load in both DomU and Dom0.
Fix the issue by mapping each non-ram page to the zero page. Keep direct
path with remap_oldmem_pfn_range() to avoid looping through all pages on
bare metal.
The issue can also be solved by overriding remap_oldmem_pfn_range() in
xen-specific code, as remap_oldmem_pfn_range() was been designed for.
That, however, would involve non-obvious xen code path for all x86 builds
with CONFIG_XEN_PVHVM=y and would prevent all other hypervisor-specific
code on x86 arch from doing the same override.
[fengguang.wu@...el.com: remap_oldmem_pfn_checked() can be static]
[akpm@...ux-foundation.org: clean up layout]
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Reviewed-by: Andrew Jones <drjones@...hat.com>
Cc: Michael Holzheu <holzheu@...ux.vnet.ibm.com>
Acked-by: Vivek Goyal <vgoyal@...hat.com>
Cc: David Vrabel <david.vrabel@...rix.com>
Signed-off-by: Fengguang Wu <fengguang.wu@...el.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Baoquan He <bhe@...hat.com>
---
fs/proc/vmcore.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 79 insertions(+), 3 deletions(-)
diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 6d7d646..0d962bc 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -294,6 +294,82 @@ static inline char *alloc_elfnotes_buf(size_t notes_sz)
* virtually contiguous user-space in ELF layout.
*/
#if defined(CONFIG_MMU) && !defined(CONFIG_S390)
+/*
+ * remap_oldmem_pfn_checked - do remap_oldmem_pfn_range replacing all pages
+ * reported as not being ram with the zero page.
+ *
+ * @vma: vm_area_struct describing requested mapping
+ * @from: start remapping from
+ * @pfn: page frame number to start remapping to
+ * @size: remapping size
+ * @prot: protection bits
+ *
+ * Returns zero on success, -EAGAIN on failure.
+ */
+static int remap_oldmem_pfn_checked(struct vm_area_struct *vma,
+ unsigned long from, unsigned long pfn,
+ unsigned long size, pgprot_t prot)
+{
+ unsigned long map_size;
+ unsigned long pos_start, pos_end, pos;
+ unsigned long zeropage_pfn = my_zero_pfn(0);
+ size_t len = 0;
+
+ pos_start = pfn;
+ pos_end = pfn + (size >> PAGE_SHIFT);
+
+ for (pos = pos_start; pos < pos_end; ++pos) {
+ if (!pfn_is_ram(pos)) {
+ /*
+ * We hit a page which is not ram. Remap the continuous
+ * region between pos_start and pos-1 and replace
+ * the non-ram page at pos with the zero page.
+ */
+ if (pos > pos_start) {
+ /* Remap continuous region */
+ map_size = (pos - pos_start) << PAGE_SHIFT;
+ if (remap_oldmem_pfn_range(vma, from + len,
+ pos_start, map_size,
+ prot))
+ goto fail;
+ len += map_size;
+ }
+ /* Remap the zero page */
+ if (remap_oldmem_pfn_range(vma, from + len,
+ zeropage_pfn,
+ PAGE_SIZE, prot))
+ goto fail;
+ len += PAGE_SIZE;
+ pos_start = pos + 1;
+ }
+ }
+ if (pos > pos_start) {
+ /* Remap the rest */
+ map_size = (pos - pos_start) << PAGE_SHIFT;
+ if (remap_oldmem_pfn_range(vma, from + len, pos_start,
+ map_size, prot))
+ goto fail;
+ }
+ return 0;
+fail:
+ do_munmap(vma->vm_mm, from, len);
+ return -EAGAIN;
+}
+
+static int vmcore_remap_oldmem_pfn(struct vm_area_struct *vma,
+ unsigned long from, unsigned long pfn,
+ unsigned long size, pgprot_t prot)
+{
+ /*
+ * Check if oldmem_pfn_is_ram was registered to avoid
+ * looping over all pages without a reason.
+ */
+ if (oldmem_pfn_is_ram)
+ return remap_oldmem_pfn_checked(vma, from, pfn, size, prot);
+ else
+ return remap_oldmem_pfn_range(vma, from, pfn, size, prot);
+}
+
static int mmap_vmcore(struct file *file, struct vm_area_struct *vma)
{
size_t size = vma->vm_end - vma->vm_start;
@@ -353,9 +429,9 @@ static int mmap_vmcore(struct file *file, struct vm_area_struct *vma)
tsz = min_t(size_t, m->offset + m->size - start, size);
paddr = m->paddr + start - m->offset;
- if (remap_oldmem_pfn_range(vma, vma->vm_start + len,
- paddr >> PAGE_SHIFT, tsz,
- vma->vm_page_prot))
+ if (vmcore_remap_oldmem_pfn(vma, vma->vm_start + len,
+ paddr >> PAGE_SHIFT, tsz,
+ vma->vm_page_prot))
goto fail;
size -= tsz;
start += tsz;
--
2.1.0
--
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