Re: [PATCH v5 4/9] KVM: MMU: introduce gfn_to_pfn_atomic() function

[Gleb Natapov]

On Tue, Jul 06, 2010 at 06:47:47PM +0800, Xiao Guangrong wrote:
> Introduce gfn_to_pfn_atomic(), it's the fast path and can used in atomic
> context, the later patch will use it
> 
> Signed-off-by: Xiao Guangrong <xiaoguangr...@cn.fujitsu.com>
> ---
>  include/linux/kvm_host.h |    1 +
>  virt/kvm/kvm_main.c      |   32 +++++++++++++++++++++++++-------
>  2 files changed, 26 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index e796326..e0fb543 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -295,6 +295,7 @@ void kvm_release_page_dirty(struct page *page);
>  void kvm_set_page_dirty(struct page *page);
>  void kvm_set_page_accessed(struct page *page);
>  
> +pfn_t gfn_to_pfn_atomic(struct kvm *kvm, gfn_t gfn);
>  pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn);
>  pfn_t gfn_to_pfn_memslot(struct kvm *kvm,
>                        struct kvm_memory_slot *slot, gfn_t gfn);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index a60b6b0..5467fe5 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -934,19 +934,25 @@ unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
>  }
>  EXPORT_SYMBOL_GPL(gfn_to_hva);
>  
> -static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr)
> +static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic)
>  {
>       struct page *page[1];
>       int npages;
>       pfn_t pfn;
>  
> -     might_sleep();
> -
> -     npages = get_user_pages_fast(addr, 1, 1, page);
> +     if (atomic)
> +             npages = __get_user_pages_fast(addr, 1, 1, page);
> +     else {
> +             might_sleep();
> +             npages = get_user_pages_fast(addr, 1, 1, page);
> +     }
>  
>       if (unlikely(npages != 1)) {
>               struct vm_area_struct *vma;
>  
> +             if (atomic)
> +                     goto return_bad_page;
> +
You are skipping hwpoison test and sometimes you will return bad_page
for something that returns good pfn now without caller even know.
vma->vm_flags & VM_PFNMAP comes to mind. Is this safe?

>               down_read(&current->mm->mmap_sem);
>               if (is_hwpoison_address(addr)) {
>                       up_read(&current->mm->mmap_sem);
> @@ -959,6 +965,7 @@ static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long 
> addr)
>               if (vma == NULL || addr < vma->vm_start ||
>                   !(vma->vm_flags & VM_PFNMAP)) {
>                       up_read(&current->mm->mmap_sem);
> +return_bad_page:
>                       get_page(bad_page);
>                       return page_to_pfn(bad_page);
>               }
> @@ -972,7 +979,7 @@ static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long 
> addr)
>       return pfn;
>  }
>  
> -pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
> +pfn_t __gfn_to_pfn(struct kvm *kvm, gfn_t gfn, bool atomic)
>  {
>       unsigned long addr;
>  
> @@ -982,7 +989,18 @@ pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
>               return page_to_pfn(bad_page);
>       }
>  
> -     return hva_to_pfn(kvm, addr);
> +     return hva_to_pfn(kvm, addr, atomic);
> +}
> +
> +pfn_t gfn_to_pfn_atomic(struct kvm *kvm, gfn_t gfn)
> +{
> +     return __gfn_to_pfn(kvm, gfn, true);
> +}
> +EXPORT_SYMBOL_GPL(gfn_to_pfn_atomic);
> +
> +pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
> +{
> +     return __gfn_to_pfn(kvm, gfn, false);
>  }
>  EXPORT_SYMBOL_GPL(gfn_to_pfn);
>  
> @@ -990,7 +1008,7 @@ pfn_t gfn_to_pfn_memslot(struct kvm *kvm,
>                        struct kvm_memory_slot *slot, gfn_t gfn)
>  {
>       unsigned long addr = gfn_to_hva_memslot(slot, gfn);
> -     return hva_to_pfn(kvm, addr);
> +     return hva_to_pfn(kvm, addr, false);
>  }
>  
>  struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
> -- 
> 1.6.1.2
> 
> 
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                        Gleb.
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