linux-kernel - Re: [Xen-devel] [PATCH v2 2/2] x86/xen: allow privcmd hypercalls to be preempted

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Message-ID: <20141211210543.GQ25677@wotan.suse.de>
Date:	Thu, 11 Dec 2014 22:05:43 +0100
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	Juergen Gross <jgross@...e.com>,
	Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Jan Beulich <JBeulich@...e.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...e.de>, bpoirier@...e.de
Subject: Re: [Xen-devel] [PATCH v2 2/2] x86/xen: allow privcmd hypercalls
	to be preempted

On Thu, Dec 11, 2014 at 11:09:42AM +0000, David Vrabel wrote:
> On 10/12/14 23:51, Andy Lutomirski wrote:
> > On Wed, Dec 10, 2014 at 3:34 PM, Luis R. Rodriguez
> > All that being said, this is IMO a bit gross.  You've added a bunch of
> > asm that's kind of like a parallel error_exit, and the error entry and
> > exit code is hairy enough that this scares me.  Can you do this mostly
> > in C instead?  This would look a nicer if it could be:
> 
> I abandoned my initial attempt that looked like this because I thought
> it was gross too.
> 
> >     call xen_evtchn_do_upcall
> >     popq %rsp
> >     CFI_DEF_CFA_REGISTER rsp
> >     decl PER_CPU_VAR(irq_count)
> > +  call xen_end_upcall
> >     jmp error_exit
> > 
> > Where xen_end_upcall would be witten in C, nokprobes and notrace (if
> > needed) and would check pt_regs and whatever else and just call
> > schedule if needed?
> 
> Oh that's a good idea, thanks!

David, are you going to respin yourself with the goal to get this upstream?
If so I can move on with life on other matters.

  Luis
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