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Commit 0692dedc authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Linus Torvalds
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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@intel.com: remap_oldmem_pfn_checked() can be static]
[akpm@linux-foundation.org: clean up layout]
Signed-off-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: default avatarAndrew Jones <drjones@redhat.com>
Cc: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Acked-by: default avatarVivek Goyal <vgoyal@redhat.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: default avatarFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 33144e84

fs/proc/vmcore.c

+79 −3
Original line number Diff line number Diff line
@@ -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;
@@ -387,7 +463,7 @@ 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,

			if (vmcore_remap_oldmem_pfn(vma, vma->vm_start + len,

						    paddr >> PAGE_SHIFT, tsz,

						    vma->vm_page_prot))

				goto fail;