Re: [Xen-devel] [PATCH] arm/monitor vm-events: Implement guest-request support

[Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>]

On 2/19/2016 4:26 PM, Jan Beulich wrote:
> > > > On 18.02.16 at 20:35, <czuzu@xxxxxxxxxxxxxxx> wrote:
> > ---
> >   MAINTAINERS                     |   1 +
> >   xen/arch/arm/hvm.c              |   8 +++
> >   xen/arch/x86/hvm/event.c        | 116 ++++++----------------------------------
> >   xen/arch/x86/hvm/hvm.c          |   1 +
> >   xen/arch/x86/monitor.c          |  14 -----
> >   xen/arch/x86/vm_event.c         |   1 +
> >   xen/common/Makefile             |   2 +-
> >   xen/common/hvm/Makefile         |   3 +-
> >   xen/common/hvm/event.c          |  96 +++++++++++++++++++++++++++++++++
> So here you _again_ try to introduce something HVM-ish for ARM.
> Why? Why can't this code live in common/vm_event.c?
Are you referring to "xen/arch/arm/hvm.c"? If so, I did not introduce 
that file, it was already there, all I did is add handling of 
HVMOP_guest_request_vm_event to ARM-side's already existing do_hvm_op :).
On the "HVM-ish" note, is there some incompatibility between ARM and the 
concept of HVM?
> > --- a/xen/include/asm-x86/domain.h
> > +++ b/xen/include/asm-x86/domain.h
> > @@ -376,17 +376,15 @@ struct arch_domain
> >       unsigned long *pirq_eoi_map;
> >       unsigned long pirq_eoi_map_mfn;
> >   
> > -    /* Monitor options */
> > +    /* Arch-specific monitor options */
> >       struct {
> > -        unsigned int write_ctrlreg_enabled       : 4;
> > -        unsigned int write_ctrlreg_sync          : 4;
> > -        unsigned int write_ctrlreg_onchangeonly  : 4;
> > -        unsigned int mov_to_msr_enabled          : 1;
> > -        unsigned int mov_to_msr_extended         : 1;
> > -        unsigned int singlestep_enabled          : 1;
> > -        unsigned int software_breakpoint_enabled : 1;
> > -        unsigned int guest_request_enabled       : 1;
> > -        unsigned int guest_request_sync          : 1;
> > +        uint16_t write_ctrlreg_enabled       : 4;
> > +        uint16_t write_ctrlreg_sync          : 4;
> > +        uint16_t write_ctrlreg_onchangeonly  : 4;
> > +        uint16_t mov_to_msr_enabled          : 1;
> > +        uint16_t mov_to_msr_extended         : 1;
> > +        uint16_t singlestep_enabled          : 1;
> > +        uint16_t software_breakpoint_enabled : 1;
> >       } monitor;
> What is this type change supposed to achieve in general, and in
> particular in the context of this patch?
Some time before this patch there was a discussion I had w/ ARM 
maintainer Ian Campbell who made the suggestion to try and move parts of 
the monitor vm-events code to the common-side.
(you can find that discussion here: 
https://www.mail-archive.com/xen-devel@xxxxxxxxxxxxx/msg54139.html).
In short, the reason for his suggestion was that that previous attempt 
of mine to add guest-request support for ARM highlighted code 
duplication between X86 and ARM if I were to leave the monitor vm-events 
code as it was (that is, completely arch-specific). In an effort to 
avoid that, I first submitted a 7 patch-series which tried to move as 
much as possible to the common-side.
"As much as possible" meant guest-request, ctrl-reg write, single-step 
and software breakpoints, all moved to the common-side. That also meant 
introducing some Kconfigs to selectively activate some parts of that 
now-common code, since not all of it was used on ARM at that moment. 
Although conceptually that code could have remained on the common-side, 
Tamas pointed out that we could get rid of the Kconfigs (which in his 
opinion bloated the code) by only moving at the moment what is 
implemented on both X86 and ARM. As for the rest, he noted that when I 
add implementations for the other monitor vm-events on ARM as well, I 
could move that to common as well. The above is a result of that - 
guest-request is implemented on both X86 and ARM with this patch, hence 
I also moved it to common.
> > --- a/xen/include/asm-x86/hvm/event.h
> > +++ b/xen/include/asm-x86/hvm/event.h
> > @@ -1,5 +1,9 @@
> >   /*
> > - * event.h: Hardware virtual machine assist events.
> > + * include/asm-x86/hvm/event.h
> > + *
> > + * Arch-specific hardware virtual machine event abstractions.
> > + *
> > + * Copyright (c) 2016, Bitdefender S.R.L.
> Is this true? Namely, was _all_ of the code here written by people
> on your company, including what may have got moved here from
> elsewhere?
>
> Jan
My bad. Removing that line would be satisfactory, yes?

Corneliu.

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