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

[Gleb Natapov <gleb@redhat.com>]

On Tue, Oct 19, 2010 at 01:05:22PM +0200, Gleb Natapov wrote:
> 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)?
> 
Works for me.

> 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.
> --
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--
			Gleb.