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

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2015-06-02 at 16:43 +0100, Andrew Cooper wrote:
> On 02/06/15 16:39, Ian Campbell wrote:
> > 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@xxxxxxxxxxxxxxx>
> >> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
> > 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.
> 
> When I suggested this, I expected each arch to maintain its own index
> space and for these spaces to all start at 0, as there is very little
> which is truly common at this level.

That's fine too, but implies that tests/xen-access.c therefore needs
some additional #ifdeffery.

Ian.



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