Re: [PATCH V8] xen/vm_event: Clean up control-register-write vm_events and add XCR0 event

[Ian Campbell <ian.campbell@citrix.com>]

On Fri, 2015-05-29 at 16:45 +0300, Razvan Cojocaru wrote:
> As suggested by Andrew Cooper, this patch attempts to remove
> some redundancy and allow for an easier time when adding vm_events
> for new control registers in the future, by having a single
> VM_EVENT_REASON_WRITE_CTRLREG vm_event type, meant to serve CR0,
> CR3, CR4 and (newly introduced) XCR0. The actual control register
> will be deduced by the new .index field in vm_event_write_ctrlreg
> (renamed from vm_event_mov_to_cr). The patch has also modified
> the xen-access.c test - it is now able to log CR3 events.
> 
> Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
> Acked-by: Jan Beulich <jbeulich@suse.com>

Seems ok from the tools and arm side, so long as the xen-access.c test
is likely to build on ARM despite the new x86-isms (it looks like it to
me) and the following Q:

> +/* Supported values for the vm_event_write_ctrlreg index. */
> +#define VM_EVENT_X86_CR0    0
> +#define VM_EVENT_X86_CR3    1
> +#define VM_EVENT_X86_CR4    2
> +#define VM_EVENT_X86_XCR0   3

Is the intention for different architectures to use non-overlapping
number spaces? (i.e. ARM would start from 0x10000 or something)?

If not then the usages in xen-access.c are a little more problematic. I
can just about tolerate a tool on arm which asks "monitor x86 cr3" and
then never sees anything, but to get events for whatever ARM reg happens
to share the index instead would be wrong I think.

Ian.