On Mon, Jul 6, 2015 at 11:54 AM, Jan Beulich <jbeul...@suse.com> wrote:
> >>> On 06.07.15 at 17:35, <tleng...@novetta.com> wrote: > > On Mon, Jul 6, 2015 at 11:26 AM, Jan Beulich <jbeul...@suse.com> wrote: > > > >> >>> On 30.06.15 at 16:40, <tleng...@novetta.com> wrote: > >> > On Tue, Jun 30, 2015 at 10:18 AM, Andrew Cooper < > >> andrew.coop...@citrix.com> > >> > wrote: > >> > > >> >> On 30/06/15 15:11, Tamas K Lengyel wrote: > >> >> > diff --git a/xen/include/public/vm_event.h > >> >> b/xen/include/public/vm_event.h > >> >> > index 577e971..b8c3dde 100644 > >> >> > --- a/xen/include/public/vm_event.h > >> >> > +++ b/xen/include/public/vm_event.h > >> >> > @@ -44,9 +44,15 @@ > >> >> > * paused > >> >> > * VCPU_PAUSED in a response signals to unpause the vCPU > >> >> > */ > >> >> > -#define VM_EVENT_FLAG_VCPU_PAUSED (1 << 0) > >> >> > -/* Flags to aid debugging mem_event */ > >> >> > -#define VM_EVENT_FLAG_FOREIGN (1 << 1) > >> >> > +#define VM_EVENT_FLAG_VCPU_PAUSED (1 << 0) > >> >> > +/* Flag to aid debugging mem_event */ > >> >> > +#define VM_EVENT_FLAG_FOREIGN (1 << 1) > >> >> > +/* > >> >> > + * Toggle singlestepping on vm_event response. > >> >> > + * Requires the vCPU to be paused already (synchronous events > only). > >> >> > + * Only supported on Intel CPUs with MTF capability. > >> >> > >> >> This sentence shouldn't be in the public API. It is a limitation of > the > >> >> current implementation, not of the API, and could be removed with > >> >> further development. > >> >> > >> > > >> > I disagree because there is no error condition returned if a user > tries > >> to > >> > use it on non-Intel hw, so the only option a user would have to figure > >> out > >> > why it's not working is reading the Xen source. IMHO the public API > >> should > >> > describe the limitations as that's what potential users will read > first. > >> > When we have hardware other then Intel that supports something like > this, > >> > we can remove the comment. > >> > >> FWIW I agree with Andrew, and if on non-Intel hardware there's > >> no error (or other indication) being returned, that's actually an > >> issue to be fixed imo. > > > > There is no opportunity for that, the current API does not provide a > > mechanism to signal failure on things that were requested on the vm_event > > response. Creating such a mechanism is beyond the scope of this patch > and I > > don't think it's necessary. IMHO the comment makes it clear that this > will > > only work on Intel hardware which suffices for now. > > You're the maintainer of the code in question, so I won't (and > can't) enforce Andrew's and my view. > > Jan > Unless Razvan have a different opinion on the matter (although he already Acked it), I think it's good as is. Thanks, Tamas
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