Re: [Xen-devel] [PATCH] vm_event: Implement ARM SMC events

[Julien Grall <julien.grall@xxxxxxx>]

Hello Corneliu,

On 13/04/16 09:55, Corneliu ZUZU wrote:
> On 4/12/2016 8:24 PM, Tamas K Lengyel wrote:
> Another issue came to my mind: "HVC #imm", if handled through the
> hvm-ops code, currently requires setting other registers to predefined
> values before the HVC is actually issued. That would imply additional
> effort to save/restore those registers if an external privileged domain
> would want to set guest breakpoints. Given that, if we were to use HVC
> for sw-bkpts, IMO it would be nice if the hvm-ops code architecture
> would be slightly changed such that -lone- "HVM #imm" calls would be
> achievable for some use cases, such as this.
That is not true. All the hypercalls are using the same #imm 
(XEN_HYPERCALL_TAG = 0xEA1), which indeed requires specific value in 
various registers to differentiate the HVM-ops.
It's up to us to define the requirements for the other #imm. For 
instance there are some #imm allocated for debugging (see do_debug_trap) 
that will dump the content of the registers.
> > So what I will do instead of issuing a software_breakpoint vm_event
> > for SMCs, I'll introduce a new type, say
> > VM_EVENT_REASON_PRIVILEGED_CALL, that can be used to forward both
> > hypercalls and SMCs to a monitoring guest. This would also allow us to
> > use the software_breakpoint type for the actual software breakpoint
> > events in the future.
> >
> > Tamas
> Isn't the HVC-part already achieved by guest-request vm-events? Maybe
> tying this vm-event specifically to SMC (in which case the name could be
> something like VM_EVENT_REASON_SECURE_CALL) and thus making it
> ARM-specific would avoid that redundancy?
I would create 2 distinct events for HVC and SMC. It would make easier 
to differentiate them in userspace.
Regards,

--
Julien Grall

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