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

[Kirill A. Shutemov]

On Tue, May 26, 2020 at 09:14:59AM +0300, Mike Rapoport wrote:
> 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.

Right, Vitaly has pointed me to this already.

-- 
 Kirill A. Shutemov