From 0692dedcf64bf3cdcfb9f6a51c70d49c8db351d2 Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov Date: Fri, 8 Aug 2014 14:22:05 -0700 Subject: 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: Vitaly Kuznetsov Reviewed-by: Andrew Jones Cc: Michael Holzheu Acked-by: Vivek Goyal Cc: David Vrabel Signed-off-by: Fengguang Wu Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/proc/vmcore.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 79 insertions(+), 3 deletions(-) (limited to 'fs') diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c index 382aa890e228..a90d6d354199 100644 --- a/fs/proc/vmcore.c +++ b/fs/proc/vmcore.c @@ -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; -- cgit v1.2.3