linux-kernel - Re: [Xen-devel] [RFC v3 2/2] x86/xen: allow privcmd hypercalls to be preempted

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Date:	Thu, 22 Jan 2015 18:56:37 +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>,
	kvm list <kvm@...r.kernel.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>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Borislav Petkov <bp@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Xen-devel] [RFC v3 2/2] x86/xen: allow privcmd hypercalls to
	be preempted

On Thu, Jan 22, 2015 at 12:55:17PM +0000, David Vrabel wrote:
> On 22/01/15 03:18, Andy Lutomirski wrote:
> >> --- a/drivers/xen/events/events_base.c
> >> +++ b/drivers/xen/events/events_base.c
> >> @@ -32,6 +32,8 @@
> >>  #include <linux/slab.h>
> >>  #include <linux/irqnr.h>
> >>  #include <linux/pci.h>
> >> +#include <linux/sched.h>
> >> +#include <linux/kprobes.h>
> >>
> >>  #ifdef CONFIG_X86
> >>  #include <asm/desc.h>
> >> @@ -1243,6 +1245,17 @@ void xen_evtchn_do_upcall(struct pt_regs *regs)
> >>         set_irq_regs(old_regs);
> >>  }
> >>
> >> +notrace void xen_end_upcall(struct pt_regs *regs)
> >> +{
> >> +       if (!xen_is_preemptible_hypercall(regs) ||
> >> +           __this_cpu_read(xed_nesting_count))
> >> +               return;
> > 
> > What's xed_nesting_count?
> 
> It used to prevent nested upcalls when a hypercall called from an upcall
> triggers another upcall.
> 
> There's no way a such a nested hypercall can be preemptible so the check
> for xed_nesting_count an be removed from here.

Removed.

  Luis
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