Re: [Xen-devel] [PATCH 2/3] xen: arm: correctly handle continuations for 64-bit guests

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Wed, 2015-03-25 at 15:41 +0000, Andrew Cooper wrote:
> On 25/03/15 15:34, Ian Campbell wrote:
> > The 64-bit ABI is different to 32-bit:
> >
> >   - uses x16 as the op register rather than r12.
> >   - arguments in x0..x5 and not r0..r5. Using rN here potentially
> >     truncates.
> >   - return value goes in x0, not r0.
> >
> > Hypercalls can only be made directly from kernel space, so checking
> > the domain's size is sufficient.
> >
> > The update of regs->pc is duplicated in both halves because the 32-bit
> > case is going to need fixing to handle Thumb mode (next patch).
> >
> > Spotted due to spurious -EFAULT when destroying a domain, due to the
> > hypercall's pointer argument being truncated. I'm unclear why I am
> > only seeing this now.
> >
> > Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> 
> Almost certainly 15e0aac6fe76be6a710a8e6d3da610d437903266 which changed 
> XEN_DOMCTL_destroydomain to use continuations rather than repeated 
> hypercalls.

That sounds like why domaindestroy now exhibits it, but not why it
hasn't been plaguing us on different hypercalls for ever. I suppose we
don't actually hit preempt very often in practice.

Ian.


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