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Date:   Wed, 27 May 2020 00:56:22 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Mike Rapoport <rppt@kernel.org>
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        David Rientjes <rientjes@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        Will Drewry <wad@chromium.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
        "Kleen, Andi" <andi.kleen@intel.com>, x86@kernel.org,
        kvm@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [RFC 06/16] KVM: Use GUP instead of copy_from/to_user() to
 access guest memory
Message-ID: <20200526215622.r455gfohtufr45vj@box>
References: <20200522125214.31348-1-kirill.shutemov@linux.intel.com>
 <20200522125214.31348-7-kirill.shutemov@linux.intel.com>
 <20200526061459.GC13247@kernel.org>
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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@linux.intel.com>
> > ---
> >  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