KVM: switch to get_user_pages_fast

Convert gfn_to_pfn to use get_user_pages_fast, which can do lockless
pagetable lookups on x86. Kernel compilation on 4-way guest is 3.7%
faster on VMX.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2907d05cfcc3..cd34f73513d3 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -723,9 +723,6 @@ unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
 }
 EXPORT_SYMBOL_GPL(gfn_to_hva);
 
-/*
- * Requires current->mm->mmap_sem to be held
- */
 pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
 {
         struct page *page[1];
@@ -741,20 +738,23 @@ pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
                 return page_to_pfn(bad_page);
         }
 
-        npages = get_user_pages(current, current->mm, addr, 1, 1, 0, page,
-                                NULL);
+        npages = get_user_pages_fast(addr, 1, 1, page);
 
         if (unlikely(npages != 1)) {
                 struct vm_area_struct *vma;
 
+                down_read(&current->mm->mmap_sem);
                 vma = find_vma(current->mm, addr);
+
                 if (vma == NULL || addr < vma->vm_start ||
                     !(vma->vm_flags & VM_PFNMAP)) {
+                        up_read(&current->mm->mmap_sem);
                         get_page(bad_page);
                         return page_to_pfn(bad_page);
                 }
 
                 pfn = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
+                up_read(&current->mm->mmap_sem);
                 BUG_ON(!is_mmio_pfn(pfn));
         } else
                 pfn = page_to_pfn(page[0]);