Re: [PATCH] KVM: arm64: Fix 64 bit mmio handle

[Schspa Shi]

Marc Zyngier <maz@xxxxxxxxxx> writes:

> On Thu, 30 Jun 2022 17:12:20 +0100,
> Schspa Shi <schspa@xxxxxxxxx> wrote:
> > If the len is 8 bytes, we can't get the correct sign extend for
> > be system.
>
> I'm afraid you'll have to give me a bit more details.
>
> > Fix the mask type len and the comparison of length.
> >
> > Signed-off-by: Schspa Shi <schspa@xxxxxxxxx>
> > ---
> >  arch/arm64/kvm/mmio.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/mmio.c b/arch/arm64/kvm/mmio.c
> > index 3dd38a151d2a6..0692f8b18f35c 100644
> > --- a/arch/arm64/kvm/mmio.c
> > +++ b/arch/arm64/kvm/mmio.c
> > @@ -81,8 +81,8 @@ unsigned long kvm_mmio_read_buf(const void 
> > *buf, unsigned int len)
> >  int kvm_handle_mmio_return(struct kvm_vcpu *vcpu)
> >  {
> >  	unsigned long data;
> > +	unsigned long mask;
> >  	unsigned int len;
> > -	int mask;
> >  
> >  	/* Detect an already handled MMIO return */
> >  	if (unlikely(!vcpu->mmio_needed))
> > @@ -97,7 +97,7 @@ int kvm_handle_mmio_return(struct kvm_vcpu 
> > *vcpu)
> >  		data = kvm_mmio_read_buf(run->mmio.data, len);
> >  
> >  		if (kvm_vcpu_dabt_issext(vcpu) &&
> > -		    len < sizeof(unsigned long)) {
> > +		    len <= sizeof(unsigned long)) {
>
> If you're reading an 8 byte quantity, what is there to 
> sign-extend?
> Sign extension only makes sense if what you're reading is 
> *smaller*
> than the size of the register you are targeting.

Yes, you are correct, sorry for my bad patch.
Please ignore this patch.

> I must be missing something. And how is that related to running 
> BE? BE
> in the host? The guest?

I mean BE is for guest running with BE mode.

> Please convince me.
>
> 	M.

--
BRs
Schspa Shi