From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: KVM PMU virtualization
Date: Wed, 03 Mar 2010 11:13:11 +0100
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Cc: Ingo Molnar <mingo@elte.hu>, Joerg Roedel <joro@8bytes.org>,
	Jes Sorensen <Jes.Sorensen@redhat.com>,
	KVM General <kvm@vger.kernel.org>, Avi Kivity <avi@redhat.com>,
	Zachary Amsden <zamsden@redhat.com>,
	Gleb Natapov <gleb@redhat.com>, ming.m.lin@intel.com
To: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
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On Wed, 2010-03-03 at 17:27 +0800, Zhang, Yanmin wrote:
> +static inline u64 perf_instruction_pointer(struct pt_regs *regs)
> +{
> +       u64 ip;
> +       ip = percpu_read(perf_virt_ip.ip);
> +       if (!ip)
> +               ip = instruction_pointer(regs);
> +       else
> +               perf_reset_virt_ip();
> +       return ip;
> +}
> +
> +static inline unsigned int perf_misc_flags(struct pt_regs *regs)
> +{
> +       if (percpu_read(perf_virt_ip.ip)) {
> +               return percpu_read(perf_virt_ip.user_mode) ?
> +                       PERF_RECORD_MISC_GUEST_USER :
> +                       PERF_RECORD_MISC_GUEST_KERNEL;
> +       } else
> +               return user_mode(regs) ? PERF_RECORD_MISC_USER :
> +                                PERF_RECORD_MISC_KERNEL;
> +} 

This codes in the assumption that perf_misc_flags() must only be called
before perf_instruction_pointer(), which is currently true, but you
might want to put a comment near to remind us of this.