Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753530AbaGKMHI (ORCPT ); Fri, 11 Jul 2014 08:07:08 -0400 Received: from mx1.redhat.com ([209.132.183.28]:63228 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752385AbaGKMHG (ORCPT ); Fri, 11 Jul 2014 08:07:06 -0400 Date: Fri, 11 Jul 2014 08:06:53 -0400 From: Vivek Goyal To: Vitaly Kuznetsov Cc: Andrew Morton , Michael Holzheu , HATAYAMA Daisuke , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] mmap_vmcore: skip non-ram pages reported by hypervisors Message-ID: <20140711120653.GA15611@redhat.com> References: <1405068552-19453-1-git-send-email-vkuznets@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1405068552-19453-1-git-send-email-vkuznets@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 11, 2014 at 10:49:12AM +0200, Vitaly Kuznetsov wrote: > 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 v3: > - multi line comment style changes > - minor code style changes > > Changes from v2: > - make remap_oldmem_pfn_checked() interface exactly match > remap_oldmem_pfn_range() > - unmap mapped part inside remap_oldmem_pfn_checked() in case of failure so > we don't need to take care of it in mmap_vmcore() > - create vmcore_remap_oldmem_pfn() wrapper > > 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 > Reviewed-by: Andrew Jones This one looks good to me. Thanks. Acked-by: Vivek Goyal Vivek > --- > fs/proc/vmcore.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 80 insertions(+), 3 deletions(-) > > diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c > index 382aa89..405a409 100644 > --- a/fs/proc/vmcore.c > +++ b/fs/proc/vmcore.c > @@ -328,6 +328,83 @@ 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. > + */ > +int remap_oldmem_pfn_checked(struct vm_area_struct *vma, unsigned long from, > + unsigned long pfn, unsigned long size, > + pgprot_t prot) > +{ > + 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, 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, vma->vm_page_prot)) > + goto fail; > + len += map_size; > + } > + return 0; > +fail: > + do_munmap(vma->vm_mm, from, len); > + return -EAGAIN; > +} > + > +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 +464,9 @@ 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; > -- > 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/