Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755066AbaGNMsI (ORCPT ); Mon, 14 Jul 2014 08:48:08 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32408 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754250AbaGNMsA (ORCPT ); Mon, 14 Jul 2014 08:48:00 -0400 From: Vitaly Kuznetsov To: "HATAYAMA\, Daisuke" Cc: Andrew Morton , Vivek Goyal , Michael Holzheu , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5] mmap_vmcore: skip non-ram pages reported by hypervisors References: <1405329417-3996-1-git-send-email-vkuznets@redhat.com> <53C3A782.9030109@jp.fujitsu.com> Date: Mon, 14 Jul 2014 14:47:46 +0200 In-Reply-To: <53C3A782.9030109@jp.fujitsu.com> (Daisuke HATAYAMA's message of "Mon, 14 Jul 2014 18:48:50 +0900") Message-ID: <87ha2kumx9.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "HATAYAMA, Daisuke" writes: > (2014/07/14 18:16), 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 v4: >> - change map_size type size_t -> unsigned long >> - use prot instead of vma->vm_page_prot inside remap_oldmem_pfn_checked() >> >> 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 >> >> Reviewed-by: Andrew Jones >> Signed-off-by: Vitaly Kuznetsov >> --- >> 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..1f77f35 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) >> +{ >> + unsigned long map_size; >> + unsigned long pos_start, pos_end, pos; >> + unsigned long zeropage_pfn = my_zero_pfn(0); >> + u64 len = 0; > > Sorry, I missed this yesterday. Thanks for your review! > This should also be fixed as size_t or unsigned long. > Does 32-bit compiler warn about this at the call of do_munmap() below > due to difference of bit length of the two types? Mine doesn't. But you're right, it makes sense to make it match do_munmap()'s interface and len there is size_t. I'll send v6 with this change. > >> + >> + 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; >> + 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; >> -- Vitaly -- 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/