Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755172AbaGHR14 (ORCPT ); Tue, 8 Jul 2014 13:27:56 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:29811 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755140AbaGHR1x (ORCPT ); Tue, 8 Jul 2014 13:27:53 -0400 Date: Tue, 8 Jul 2014 12:29:30 -0400 From: Konrad Rzeszutek Wilk To: Vitaly Kuznetsov Cc: Andrew Morton , Michael Holzheu , Vivek Goyal , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org Subject: Re: [Xen-devel] [PATCH] mmap_vmcore: skip non-ram pages reported by hypervisors Message-ID: <20140708162930.GC9727@laptop.dumpdata.com> References: <1404745549-16023-1-git-send-email-vkuznets@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1404745549-16023-1-git-send-email-vkuznets@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-Source-IP: acsinet21.oracle.com [141.146.126.237] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 07, 2014 at 05:05:49PM +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. Could the 'remap_oldmem_pfn_range' become an function ops? I see there is an 'register_oldmem_pfn_is_ram' - so could there be similar one for 'pfn_range'? > > Signed-off-by: Vitaly Kuznetsov > --- > fs/proc/vmcore.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++----- > 1 file changed, 62 insertions(+), 6 deletions(-) > > diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c > index 382aa89..2716e19 100644 > --- a/fs/proc/vmcore.c > +++ b/fs/proc/vmcore.c > @@ -328,6 +328,46 @@ static inline char *alloc_elfnotes_buf(size_t notes_sz) > * virtually contiguous user-space in ELF layout. > */ > #ifdef CONFIG_MMU > +static u64 remap_oldmem_pfn_checked(struct vm_area_struct *vma, u64 len, > + unsigned long pfn, unsigned long page_count) > +{ > + unsigned long pos; > + size_t size; > + unsigned long vma_addr; > + unsigned long emptypage_pfn = __pa(empty_zero_page) >> PAGE_SHIFT; > + > + for (pos = pfn; (pos - pfn) <= page_count; pos++) { > + if (!pfn_is_ram(pos) || (pos - pfn) == page_count) { > + /* we hit a page which is not ram or reached the end */ > + if (pos - pfn > 0) { > + /* remapping continuous region */ > + size = (pos - pfn) << PAGE_SHIFT; > + vma_addr = vma->vm_start + len; > + if (remap_oldmem_pfn_range(vma, vma_addr, > + pfn, size, > + vma->vm_page_prot)) > + return len; > + len += size; > + page_count -= (pos - pfn); > + } > + if (page_count > 0) { > + /* we hit a page which is not ram, replacing > + with an empty one */ > + vma_addr = vma->vm_start + len; > + if (remap_oldmem_pfn_range(vma, vma_addr, > + emptypage_pfn, > + PAGE_SIZE, > + vma->vm_page_prot)) > + return len; > + len += PAGE_SIZE; > + pfn = pos + 1; > + page_count--; > + } > + } > + } > + return len; > +} > + > static int mmap_vmcore(struct file *file, struct vm_area_struct *vma) > { > size_t size = vma->vm_end - vma->vm_start; > @@ -383,17 +423,33 @@ static int mmap_vmcore(struct file *file, struct vm_area_struct *vma) > > list_for_each_entry(m, &vmcore_list, list) { > if (start < m->offset + m->size) { > - u64 paddr = 0; > + u64 paddr = 0, original_len; > + unsigned long pfn, page_count; > > 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) { > + pfn = paddr >> PAGE_SHIFT; > + page_count = tsz >> PAGE_SHIFT; > + original_len = len; > + len = remap_oldmem_pfn_checked(vma, len, pfn, > + page_count); > + 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@lists.xen.org > http://lists.xen.org/xen-devel -- 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/