Re: [Xen-devel] [PATCH v17 13/13] x86/domctl: Don't pause the whole domain if only getting vcpu state

[Isaila Alexandru <aisaila@xxxxxxxxxxxxxxx>]

On Lu, 2018-09-03 at 16:36 +0200, Roger Pau Monné wrote:
> On Fri, Aug 31, 2018 at 04:56:21PM +0300, Isaila Alexandru wrote:
> > 
> > On Mi, 2018-08-29 at 08:13 -0600, Jan Beulich wrote:
> > > 
> > > > 
> > > > 
> > > > > 
> > > > > 
> > > > > > 
> > > > > > 
> > > > > > On 29.08.18 at 16:02, <aisaila@xxxxxxxxxxxxxxx> wrote:
> > > > On Mi, 2018-08-22 at 18:15 +0300, Isaila Alexandru wrote:
> > > > > 
> > > > > 
> > > > > On Mi, 2018-08-22 at 16:41 +0200, Roger Pau Monné wrote:
> > > > > > 
> > > > > > 
> > > > > > If you look at vcpu_hvm in tools/libxc/xc_dom_x86.c it
> > > > > > saves
> > > > > > the
> > > > > > full
> > > > > > domain context just to get the CPU and the MTRR state of
> > > > > > VCPU#0. Do
> > > > > > you think you could switch this code to use the newly
> > > > > > introduced
> > > > > > machinery to save a single instance of a specific type?
> > > > > Sure, I will add a tool patch at the end of the series
> > > > Is this urgent to be in this series? If not I will add a new
> > > > patch
> > > > after it is all in. 
> > > Considering the problems that there have been with this series,
> > > anything to help build confidence in things still working for all
> > > cases would help here, so I'm pretty glad Roger thought of this,
> > > and while I wouldn't make it as strong as "the series can't go
> > > in without this", I'd still much prefer if you too the time.
> > I don't think it is possible to use getcontext_partial()
> > in vcpu_hvm()
> > because of the need to have a header for xc_domain_hvm_setcontext()
> > and
> > the only way to get it is by xc_domain_hvm_getcontext(). There is
> > also
> > a comment there that states the same thing
> > "/*
> >      * Get the full HVM context in order to have the header, it is
> > not
> >      * possible to get the header with getcontext_partial, and
> > crafting
> > one
> >      * from userspace is also not an option since cpuid is trapped
> > and
> >      * modified by Xen.
> >      */
> > "
> > I hope I understood the request correctly to start with and if not
> > please clarify. 
> But I expect you also get such header when fetching the state of a
> single device, or else how do you use this new hypercall in
> conjunction with xc_domain_hvm_setcontext?
> 
The new *save_one functions are based on the
old xc_domain_hvm_getcontext_partial() that did not send the header. I
had no requests to change this behavior by this point.

Thanks, 
Alex

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