Re: KVM: attempt async pf only if address is contained in vma

[Gleb Natapov <gleb@redhat.com>]

On Mon, Oct 18, 2010 at 08:24:03PM -0200, Marcelo Tosatti wrote:
> 
> Only attempt async pagefault if address is contained within vma.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 5d57ec9..a9cfbd2 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -996,8 +996,9 @@ static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic,
>  
>  		if (vma == NULL || addr < vma->vm_start ||
>  		    !(vma->vm_flags & VM_PFNMAP)) {
> -			if (async && !(vma->vm_flags & VM_PFNMAP) &&
> -			    (vma->vm_flags & VM_WRITE))
> +			if (async && vma && !(vma->vm_flags & VM_PFNMAP) &&
actually we should check for addr < vma->vm_start here too. find_vma()
is very strange function.

What about patch below (only compile tested for now)?

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 796b06e..29e40e5 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -954,6 +954,12 @@ unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
 }
 EXPORT_SYMBOL_GPL(gfn_to_hva);
 
+static pfn_t get_fault_pfn(void)
+{
+	get_page(fault_page);
+	return fault_pfn;
+}
+
 static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic,
 			bool *async)
 {
@@ -983,7 +989,7 @@ static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic,
 		struct vm_area_struct *vma;
 
 		if (atomic)
-			goto return_fault_page;
+			return get_fault_pfn();
 
 		down_read(&current->mm->mmap_sem);
 		if (is_hwpoison_address(addr)) {
@@ -992,22 +998,20 @@ static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic,
 			return page_to_pfn(hwpoison_page);
 		}
 
-		vma = find_vma(current->mm, addr);
+		vma = find_vma_intersection(current->mm, addr, addr+1);
 
-		if (vma == NULL || addr < vma->vm_start ||
-		    !(vma->vm_flags & VM_PFNMAP)) {
-			if (async && !(vma->vm_flags & VM_PFNMAP) &&
-			    (vma->vm_flags & VM_WRITE))
+		if (vma == NULL)
+			return get_fault_pfn();
+		if ((vma->vm_flags & VM_PFNMAP)) {
+			pfn = ((addr - vma->vm_start) >> PAGE_SHIFT) +
+				vma->vm_pgoff;
+			BUG_ON(!kvm_is_mmio_pfn(pfn));
+		} else {
+			if (async && (vma->vm_flags & VM_WRITE))
 				*async = true;
-			up_read(&current->mm->mmap_sem);
-return_fault_page:
-			get_page(fault_page);
-			return page_to_pfn(fault_page);
+			pfn = get_fault_pfn();
 		}
-
-		pfn = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 		up_read(&current->mm->mmap_sem);
-		BUG_ON(!kvm_is_mmio_pfn(pfn));
 	} else
 		pfn = page_to_pfn(page[0]);
 
--
			Gleb.