linux-kernel - Re: [PATCH v6 07/12] Add async PF initialization to PV guest.

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Message-ID: <20101008075414.GB8354@redhat.com>
Date:	Fri, 8 Oct 2010 09:54:14 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu,
	a.p.zijlstra@...llo.nl, tglx@...utronix.de, hpa@...or.com,
	riel@...hat.com, cl@...ux-foundation.org, mtosatti@...hat.com
Subject: Re: [PATCH v6 07/12] Add async PF initialization to PV guest.

On Thu, Oct 07, 2010 at 02:50:49PM +0200, Avi Kivity wrote:
>  On 10/04/2010 05:56 PM, Gleb Natapov wrote:
> >Enable async PF in a guest if async PF capability is discovered.
> >
> >
> >+void __cpuinit kvm_guest_cpu_init(void)
> >+{
> >+	if (!kvm_para_available())
> >+		return;
> >+
> >+	if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF)&&  kvmapf) {
> >+		u64 pa = __pa(&__get_cpu_var(apf_reason));
> >+
> >+		if (native_write_msr_safe(MSR_KVM_ASYNC_PF_EN,
> >+					  pa | KVM_ASYNC_PF_ENABLED, pa>>  32))
> 
> native_ versions of processor accessors shouldn't be used generally.
> 
> Also, the MSR isn't documented to fail on valid input, so you can
> use a normal wrmsrl() here.
> 
Kernel will oops on wrong write then. OK, why not.

> >+			return;
> >+		__get_cpu_var(apf_reason).enabled = 1;
> >+		printk(KERN_INFO"KVM setup async PF for cpu %d\n",
> >+		       smp_processor_id());
> >+	}
> >+}
> >+
> >
> >+static int kvm_pv_reboot_notify(struct notifier_block *nb,
> >+				unsigned long code, void *unused)
> >+{
> >+	if (code == SYS_RESTART)
> >+		on_each_cpu(kvm_pv_disable_apf, NULL, 1);
> >+	return NOTIFY_DONE;
> >+}
> >+
> >+static struct notifier_block kvm_pv_reboot_nb = {
> >+	.notifier_call = kvm_pv_reboot_notify,
> >+};
> 
> Does this handle kexec?
> 
Yes.

> >+
> >+static void kvm_guest_cpu_notify(void *dummy)
> >+{
> >+	if (!dummy)
> >+		kvm_guest_cpu_init();
> >+	else
> >+		kvm_pv_disable_apf(NULL);
> >+}
> 
> Why are you making decisions based on a dummy input?
> 
> The whole thing looks strange.  Use two functions?
> 
What is so strange? Type of notification is passed as a parameter.
The code that does this is just under the function. I can rename
dummy to something else. Or make it two functions.

--
			Gleb.
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