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    Subject[PATCH 22/25] KVM: opencode gfn_to_page in kvm_vm_fault
    Date
    From: Marcelo Tosatti <mtosatti@redhat.com>

    kvm_vm_fault is invoked with mmap_sem held in read mode. Since gfn_to_page
    will be converted to get_user_pages_fast, which requires this lock NOT
    to be held, switch to opencoded get_user_pages.

    Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
    Signed-off-by: Avi Kivity <avi@redhat.com>
    ---
    virt/kvm/kvm_main.c | 19 ++++++++++++-------
    1 files changed, 12 insertions(+), 7 deletions(-)

    diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
    index f42d5c2..2907d05 100644
    --- a/virt/kvm/kvm_main.c
    +++ b/virt/kvm/kvm_main.c
    @@ -1394,17 +1394,22 @@ out:

    static int kvm_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
    {
    + struct page *page[1];
    + unsigned long addr;
    + int npages;
    + gfn_t gfn = vmf->pgoff;
    struct kvm *kvm = vma->vm_file->private_data;
    - struct page *page;

    - if (!kvm_is_visible_gfn(kvm, vmf->pgoff))
    + addr = gfn_to_hva(kvm, gfn);
    + if (kvm_is_error_hva(addr))
    return VM_FAULT_SIGBUS;
    - page = gfn_to_page(kvm, vmf->pgoff);
    - if (is_error_page(page)) {
    - kvm_release_page_clean(page);
    +
    + npages = get_user_pages(current, current->mm, addr, 1, 1, 0, page,
    + NULL);
    + if (unlikely(npages != 1))
    return VM_FAULT_SIGBUS;
    - }
    - vmf->page = page;
    +
    + vmf->page = page[0];
    return 0;
    }

    --
    1.6.0.1


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