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

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Ian,

On 25/03/2015 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.
Good catch!

x16 would still contain the valid operation, because we are (most of the 
time?) continuing on the same hypercall.
So the only issue would be argument truncation. I guess that we don't 
have big value (i.e > 32 bits) to store.
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> ---
> I imagine this needs backporting everywhere...
Agree for Xen 4.4 and Xen 4.5.

Reviewed-by: Julien Grall <julien.grall@xxxxxxxxxx>

Regards,

--
Julien Grall

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