From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752849AbeDOVzE (ORCPT ); Sun, 15 Apr 2018 17:55:04 -0400 Received: from smtp-fw-6002.amazon.com ([52.95.49.90]:24005 "EHLO smtp-fw-6002.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751489AbeDOVyz (ORCPT ); Sun, 15 Apr 2018 17:54:55 -0400 X-IronPort-AV: E=Sophos;i="5.48,456,1517875200"; d="scan'208";a="339950784" From: KarimAllah Ahmed To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, pbonzini@redhat.com, rkrcmar@redhat.com Cc: Filippo Sironi , KarimAllah Ahmed Subject: [PATCH v2 04/12] X86/KVM: Handle PFNs outside of kernel reach when touching GPTEs Date: Sun, 15 Apr 2018 23:53:10 +0200 Message-Id: <1523829198-13236-5-git-send-email-karahmed@amazon.de> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1523829198-13236-1-git-send-email-karahmed@amazon.de> References: <1523829198-13236-1-git-send-email-karahmed@amazon.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Filippo Sironi cmpxchg_gpte() calls get_user_pages_fast() to retrieve the number of pages and the respective struct page to map in the kernel virtual address space. This doesn't work if get_user_pages_fast() is invoked with a userspace virtual address that's backed by PFNs outside of kernel reach (e.g., when limiting the kernel memory with mem= in the command line and using /dev/mem to map memory). If get_user_pages_fast() fails, look up the VMA that back the userspace virtual address, compute the PFN and the physical address, and map it in the kernel virtual address space with memremap(). Signed-off-by: Filippo Sironi Signed-off-by: KarimAllah Ahmed --- arch/x86/kvm/paging_tmpl.h | 38 +++++++++++++++++++++++++++++--------- 1 file changed, 29 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h index 6288e9d..31a37e4 100644 --- a/arch/x86/kvm/paging_tmpl.h +++ b/arch/x86/kvm/paging_tmpl.h @@ -141,15 +141,35 @@ static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, struct page *page; npages = get_user_pages_fast((unsigned long)ptep_user, 1, 1, &page); - /* Check if the user is doing something meaningless. */ - if (unlikely(npages != 1)) - return -EFAULT; - - table = kmap_atomic(page); - ret = CMPXCHG(&table[index], orig_pte, new_pte); - kunmap_atomic(table); - - kvm_release_page_dirty(page); + if (likely(npages == 1)) { + table = kmap_atomic(page); + ret = CMPXCHG(&table[index], orig_pte, new_pte); + kunmap_atomic(table); + + kvm_release_page_dirty(page); + } else { + struct vm_area_struct *vma; + unsigned long vaddr = (unsigned long)ptep_user & PAGE_MASK; + unsigned long pfn; + unsigned long paddr; + + down_read(¤t->mm->mmap_sem); + vma = find_vma_intersection(current->mm, vaddr, vaddr + PAGE_SIZE); + if (!vma || !(vma->vm_flags & VM_PFNMAP)) { + up_read(¤t->mm->mmap_sem); + return -EFAULT; + } + pfn = ((vaddr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; + paddr = pfn << PAGE_SHIFT; + table = memremap(paddr, PAGE_SIZE, MEMREMAP_WB); + if (!table) { + up_read(¤t->mm->mmap_sem); + return -EFAULT; + } + ret = CMPXCHG(&table[index], orig_pte, new_pte); + memunmap(table); + up_read(¤t->mm->mmap_sem); + } return (ret != orig_pte); } -- 2.7.4