Re: [Xen-devel] [PATCH v2 for-4.8] x86/hvm: Don't truncate the hvm hypercall index before range checking it

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Oct 27, 2016 at 04:05:44PM +0100, Andrew Cooper wrote:
> c/s 5eeca68f introduced the 64bit ABI for HVM guests, and chose to explicitly
> truncate the index, despite the fact that the `mov $imm32, %eax` in the
> hypercall page already provides the expected truncation.
> 
> The truncation isn't very obvious, and is counterintuitive, seeing as all
> other 64bit parameters are passed without truncation.  It is also different to
> the PV ABI, which is otherwise identical.
> 
> As the hypercall page has always been present for HVM guests (and indeed, is
> basically mandatory to abstract away vendor differences), it is exceedingly
> unlikely that any code exists which enters hvm_do_hypercall() with upper bits
> set in %rax.
> 
> Therefore, take the opportunity to fix the ABI before it becomes impossible to
> fix.
> 
> While tweaking this area, fix one piece of trailing whitespace.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Release-acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

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