Re: [PATCH v4 04/12] iommu/vt-d: Add 256-bit invalidation descriptor support

[Lu Baolu]

On 11/8/18 1:48 PM, Liu, Yi L wrote:
> > From: Liu, Yi L
> > Sent: Thursday, November 8, 2018 1:45 PM
> > > > > > > +			memcpy(desc, qi->desc + (wait_index << shift),
> > > > > >
> > > > > > Would "memcpy(desc, (unsigned long long) (qi->desc +  (wait_index
> > > > > > << shift)," be more safe?
> > > > >
> > > > > Can that be compiled? memcpy() requires a "const void *" for the
> > > > > second
> > > parameter.
> > > > > By the way, why it's safer with this casting?
> > > >
> > > > This is just an example. My point is the possibility that "qi->desc
> > > > + (wait_index <<
> > > shift)"
> > > > would be treated as "qi->desc plus (wait_index <<
> > > > shift)*sizeof(*qi->desc)". Is it possible for kernel build?
> > >
> > > qi->desc is of type of "void *".
> >
> > no, I donât think so... Refer to the code below. Even it has no correctness issue her,
> > It's not due to qi->desc is "void *" type...
> >
> > struct qi_desc {
> > -	u64 low, high;
> > +	u64 qw0;
> > +	u64 qw1;
> > +	u64 qw2;
> > +	u64 qw3;
> > };
>
> Oops, just see you modified it to be "void *" in this patch. Ok, then this is fair enough.

Yes. :-)

Best regards,
Lu Baolu