[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v2] 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. Changes from v1: - comment style changes - change remap_oldmem_pfn_checked() interface to closer match the remap_oldmem_pfn() interface - preserve formal parameters within the loop, make the loop conditions easier to understand - use my_zero_pfn() for the zero page - return remapped length instead of new offset Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Reviewed-by: Andrew Jones <drjones@xxxxxxxxxx> --- fs/proc/vmcore.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 84 insertions(+), 5 deletions(-) diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c index 382aa89..5cd13f8 100644 --- a/fs/proc/vmcore.c +++ b/fs/proc/vmcore.c @@ -328,6 +328,67 @@ 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 replacing all pages reported + * as not being ram with the zero page. + * + * @vma: vm_area_struct describing requested mapping + * @vma_addr: start remapping from + * @pfn: page frame number to start remapping to + * @size: remapping size + * + * Returns the remapped length. If no errors were hit during the remapping it + * should be equal to size. + */ +static u64 remap_oldmem_pfn_checked(struct vm_area_struct *vma, + unsigned long vma_addr, unsigned long pfn, + unsigned long size) +{ + size_t map_size; + unsigned long pos_start, pos_end, pos; + unsigned long zeropage_pfn = my_zero_pfn(0); + u64 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, vma_addr + len, + pos_start, map_size, + vma->vm_page_prot)) + return len; + len += map_size; + } + /* Remap the zero page */ + if (remap_oldmem_pfn_range(vma, vma_addr + len, + zeropage_pfn, + PAGE_SIZE, + vma->vm_page_prot)) + return len; + 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, vma_addr + len, pos_start, + map_size, + vma->vm_page_prot)) + return len; + len += map_size; + } + return len; +} + static int mmap_vmcore(struct file *file, struct vm_area_struct *vma) { size_t size = vma->vm_end - vma->vm_start; @@ -387,13 +448,31 @@ 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)) - goto fail; + + /* Check if oldmem_pfn_is_ram was registered to avoid + looping over all pages without a reason. */ + if (oldmem_pfn_is_ram) { + u64 original_len; + unsigned long pfn, vma_addr; + + pfn = paddr >> PAGE_SHIFT; + vma_addr = vma->vm_start + len; + original_len = len; + len += remap_oldmem_pfn_checked(vma, vma_addr, + pfn, tsz); + if (len != original_len + tsz) + goto fail; + } else { + if (remap_oldmem_pfn_range(vma, + vma->vm_start + len, + paddr >> PAGE_SHIFT, + tsz, + vma->vm_page_prot)) + goto fail; + len += tsz; + } size -= tsz; start += tsz; - len += tsz; if (size == 0) return 0; -- 1.9.3 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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