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fs/proc/vmcore.c:mmap_vmcore: skip non-ram pages reported by hypervisors

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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@intel.com: remap_oldmem_pfn_checked() can be static]
[akpm@linux-foundation.org: clean up layout]
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Cc: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Vitaly Kuznetsov 2014-08-08 14:22:05 -07:00 committed by Linus Torvalds
parent 33144e8429
commit 0692dedcf6
1 changed files with 79 additions and 3 deletions
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82
fs/proc/vmcore.c
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@ -328,6 +328,82 @@ static inline char *alloc_elfnotes_buf(size_t notes_sz)
* virtually contiguous user-space in ELF layout.
*/
#ifdef CONFIG_MMU
/*
* 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;
@ -387,9 +463,9 @@ 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;