linux-kernel - Re: [Xen-devel] [PATCH v5 1/2] xen: add xen_is_preemptible

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Date:	Tue, 3 Feb 2015 19:03:34 +0100
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
	xen-devel@...ts.xenproject.org, Borislav Petkov <bp@...e.de>,
	kvm@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org,
	rostedt@...dmis.org, Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...hat.com>,
	Jan Beulich <JBeulich@...e.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	paulmck@...ux.vnet.ibm.com
Subject: Re: [Xen-devel] [PATCH v5 1/2] xen: add
	xen_is_preemptible_hypercall()

On Tue, Feb 03, 2015 at 11:05:15AM +0000, David Vrabel wrote:
> On 27/01/15 01:51, Luis R. Rodriguez wrote:
> > 
> > +#ifndef CONFIG_PREEMPT
> > +extern struct { char _entry[32]; } preemptible_hypercall_page[];
> > +
> > +static inline bool xen_is_preemptible_hypercall(struct pt_regs *regs)
> > +{
> > +	return !user_mode_vm(regs) &&
> > +		regs->ip >= (unsigned long)preemptible_hypercall_page &&
> > +		regs->ip < (unsigned long)preemptible_hypercall_page + PAGE_SIZE;
> 
> I asked for this test to be optimized.
> 
> 	return (regs->ip >> PAGE_SHIFT)
>             == ((unsigned long)preemptible_hypercall_page >> PAGE_SHIFT)
> 	    && !user_mode_vm(regs);

It didn't seem you were so sure about it and I asked some
clarifications about it but you had not replied:

http://www.gossamer-threads.com/lists/xen/devel/363565?page=last

 Luis
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