Re: [Xen-devel] [RFC v2 3/6] xen/arm: Allow platform_hvc to handle guest SMC calls

[Julien Grall <julien.grall@xxxxxxx>]

Hi Tamas,

On 07/02/2017 20:38, Tamas K Lengyel wrote:
> On Tue, Feb 7, 2017 at 12:42 PM, Edgar E. Iglesias
> <edgar.iglesias@xxxxxxxxx <mailto:edgar.iglesias@xxxxxxxxx>> wrote:
>
>     From: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxxxxx
>     <mailto:edgar.iglesias@xxxxxxxxxx>>
>
>     Allow platform_hvc to handle guest SMC calls (as well as
>     HVC calls) in a platform specific way.
>
>     Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xxxxxxxxxx
>     <mailto:edgar.iglesias@xxxxxxxxxx>>
>     ---
>      xen/arch/arm/traps.c | 5 +++++
>      1 file changed, 5 insertions(+)
>
>     diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
>     index 33950d9..1bedc6e 100644
>     --- a/xen/arch/arm/traps.c
>     +++ b/xen/arch/arm/traps.c
>     @@ -2623,6 +2623,11 @@ static void do_trap_smc(struct cpu_user_regs
>     *regs, const union hsr hsr)
>          if ( current->domain->arch.monitor.privileged_call_enabled )
>              rc = monitor_smc();
>
>
> I think you should check that rc is still 0 at this point as the vCPU
> might already be paused and the event forwarded to a monitor subscriber.
SMC are used to access the secure firmware (e.g power management) and 
will be used by the guest to access the secure firmware. Today, the code 
is expecting all event to be trapped by the monitor app and software 
emulated. However, some SMCs may be needed to be forwarded to the secure 
firmware, how do you expect it to work together?
It is something I already brought up when SMC trap was added and it is 
probably time to figure out what to do because this will not be the 
first series bringing the problem. For instance if you want to do video 
decoding or even payment on Android you may need to access the secure 
firmware for cryptography. At the same time, you also want to be able to 
monitor your guest.
Cheers,

--
Julien Grall

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