Re: [RFC 06/16] KVM: Use GUP instead of copy_from/to_user() to access guest memory

[Mike Rapoport]

On Fri, May 22, 2020 at 03:52:04PM +0300, Kirill A. Shutemov wrote:
> New helpers copy_from_guest()/copy_to_guest() to be used if KVM memory
> protection feature is enabled.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
>  include/linux/kvm_host.h |  4 +++
>  virt/kvm/kvm_main.c      | 78 ++++++++++++++++++++++++++++++++++------
>  2 files changed, 72 insertions(+), 10 deletions(-)
> 
>  static int __kvm_read_guest_page(struct kvm_memory_slot *slot, gfn_t gfn,
> -				 void *data, int offset, int len)
> +				 void *data, int offset, int len,
> +				 bool protected)
>  {
>  	int r;
>  	unsigned long addr;
> @@ -2257,7 +2297,10 @@ static int __kvm_read_guest_page(struct kvm_memory_slot *slot, gfn_t gfn,
>  	addr = gfn_to_hva_memslot_prot(slot, gfn, NULL);
>  	if (kvm_is_error_hva(addr))
>  		return -EFAULT;
> -	r = __copy_from_user(data, (void __user *)addr + offset, len);
> +	if (protected)
> +		r = copy_from_guest(data, addr + offset, len);
> +	else
> +		r = __copy_from_user(data, (void __user *)addr + offset, len);

Maybe always use copy_{from,to}_guest() and move the 'if (protected)'
there?
If kvm is added to memory slot, it cab be the passed to copy_{to,from}_guest.

>  	if (r)
>  		return -EFAULT;
>  	return 0;
> @@ -2268,7 +2311,8 @@ int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
>  {
>  	struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
>  
> -	return __kvm_read_guest_page(slot, gfn, data, offset, len);
> +	return __kvm_read_guest_page(slot, gfn, data, offset, len,
> +				     kvm->mem_protected);
>  }
>  EXPORT_SYMBOL_GPL(kvm_read_guest_page);
>  
> @@ -2277,7 +2321,8 @@ int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data,
>  {
>  	struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
>  
> -	return __kvm_read_guest_page(slot, gfn, data, offset, len);
> +	return __kvm_read_guest_page(slot, gfn, data, offset, len,
> +				     vcpu->kvm->mem_protected);
>  }
>  EXPORT_SYMBOL_GPL(kvm_vcpu_read_guest_page);
>  

-- 
Sincerely yours,
Mike.