On Fri, 8 Dec 2017, Julien Grall wrote:
> On 8 Dec 2017 22:26, "Stefano Stabellini" <sstabell...@kernel.org> wrote:
> On Fri, 8 Dec 2017, Julien Grall wrote:
> > On 06/12/17 12:27, Julien Grall wrote:
> > > On 12/06/2017 01:26 AM, Stefano Stabellini wrote:
> > > > On Thu, 23 Nov 2017, Julien Grall wrote:
> > > > > Hi Andrew,
> > > > >
> > > > > On 23/11/17 18:49, Andrew Cooper wrote:
> > > > > > On 23/11/17 18:32, Julien Grall wrote:
> > > > > > > This new function will be used in a follow-up patch to copy
> data to
> > > > > > > the
> > > > > > > guest
> > > > > > > using the IPA (aka guest physical address) and then clean
> the cache.
> > > > > > >
> > > > > > > Signed-off-by: Julien Grall <julien.gr...@linaro.org>
> > > > > > > ---
> > > > > > > xen/arch/arm/guestcopy.c | 10 ++++++++++
> > > > > > > xen/include/asm-arm/guest_access.h | 6 ++++++
> > > > > > > 2 files changed, 16 insertions(+)
> > > > > > >
> > > > > > > diff --git a/xen/arch/arm/guestcopy.c
> b/xen/arch/arm/guestcopy.c
> > > > > > > index be53bee559..7958663970 100644
> > > > > > > --- a/xen/arch/arm/guestcopy.c
> > > > > > > +++ b/xen/arch/arm/guestcopy.c
> > > > > > > @@ -110,6 +110,16 @@ unsigned long raw_copy_from_guest(void
> *to,
> > > > > > > const
> > > > > > > void __user *from, unsigned le
> > > > > > > COPY_from_guest | COPY_linear);
> > > > > > > }
> > > > > > > +unsigned long copy_to_guest_phys_flush_dcache(struct
> domain *d,
> > > > > > > + paddr_t gpa,
> > > > > > > + void *buf,
> > > > > > > + unsigned int
> len)
> > > > > > > +{
> > > > > > > + /* P2M is shared between all vCPUs, so the vCPU used
> does not
> > > > > > > matter.
> > > > > > > */
> > > > > >
> > > > > > Be very careful with this line of thinking. It is only works
> after
> > > > > > DOMCTL_max_vcpus has succeeded, and before that point, it is
> a latent
> > > > > > NULL pointer dereference.
> > > > >
> > > > > I really don't expect that function been used before
> DOMCT_max_vcpus is
> > > > > set.
> > > > > It is only used for hardware emulation or Xen loading image
> into the
> > > > > hardware
> > > > > domain memory. I could add a check d->vcpus to be safe.
> > > > >
> > > > > >
> > > > > > Also, what about vcpus configured with alternative views?
> > > > >
> > > > > It is not important because the underlying call is
> get_page_from_gfn
> > > > > that does
> > > > > not care about the alternative view (that function take a
> domain in
> > > > > parameter). I can update the comment.
> > > > Since this is a new function, would it make sense to take a struct
> > > > vcpu* as parameter, instead of a struct domain* ?
> > >
> > > Well, I suggested this patch this way because likely everyone will
> use with
> > > d->vcpus[0]. And then you would have to wonder why d->vcpus[0] and
> not
> > > d->vcpus[1]...
> >
> > Thinking a bit more to this, it might be better/safer to pass either
> a domain
> > or a vCPU to copy_guest. I can see 2 solutions:
> > 1# Introduce a union that use the same parameter:
> > union
> > {
> > struct
> > {
> > struct domain *d;
> > } ipa;
> > struct
> > {
> > struct vcpu *v;
> > } gva;
> > }
> > The structure here would be to ensure that it is clear that
> only
> > domain (resp. vcpu) should be used with ipa (resp. gva).
> >
> > 2# Have 2 parameters, vcpu and domain.
> >
> > Any opinions?
>
> I think that would be clearer. You could also add a paddr_t/vaddr_t
> correspondingly inside the union maybe.
>
>
> Well, you will have nameclash happening I think.
>
>
> And vaddr_t and paddr_t are confusing because you don't know which address
> you speak about (guest vs hypervisor). At least ipa/gpa, gva are known naming.
That's not what I meant. ipa and gva are good names.
I was suggesting to put an additional address field inside the union to
avoid the issue with paddr_t and vaddr_t discussed elsewhere
(alpine.DEB.2.10.1712081313070.8052@sstabellini-ThinkPad-X260).
I am happy either way, it was just a suggestion.
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