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. > > Jan > 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. Tamas
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