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

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Date:	Tue, 3 Feb 2015 11:05:15 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	<david.vrabel@...rix.com>, <konrad.wilk@...cle.com>,
	<boris.ostrovsky@...cle.com>, <xen-devel@...ts.xenproject.org>
CC:	Borislav Petkov <bp@...e.de>, <kvm@...r.kernel.org>,
	"Luis R. Rodriguez" <mcgrof@...e.com>, <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 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);

David
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