linux-kernel - Re: [kvm-devel] [PATCH 2/3] kvmclock

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Message-ID: <473993B3.4060508@qumranet.com>
Date:	Tue, 13 Nov 2007 14:08:19 +0200
From:	Izik Eidus <izike@...ranet.com>
To:	Glauber de Oliveira Costa <gcosta@...hat.com>
CC:	"Dong, Eddie" <eddie.dong@...el.com>,
	kvm-devel@...ts.sourceforge.net, jeremy@...p.org,
	linux-kernel@...r.kernel.org, hollisb@...ibm.com, avi@...ranet.com
Subject: Re: [kvm-devel] [PATCH 2/3] kvmclock - the host part.

Glauber de Oliveira Costa wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Dong, Eddie escreveu:
>   
>>> +static void kvm_write_guest_time(struct kvm_vcpu *vcpu) +{
>>> +	struct timespec ts;
>>> +	int r;
>>> +
>>> +	if (!vcpu->clock_gpa)
>>> +		return;
>>> +
>>> +	/* Updates version to the next odd number, indicating
>>> we're writing */
>>> +	vcpu->hv_clock.version++;
>>> +	kvm_write_guest(vcpu->kvm, vcpu->clock_gpa,
>>> &vcpu->hv_clock, PAGE_SIZE);
>>> +
>>> +	kvm_get_msr(vcpu, MSR_IA32_TIME_STAMP_COUNTER,
>>> +			  &vcpu->hv_clock.last_tsc);
>>> +
>>> +	ktime_get_ts(&ts);
>>>       
>> Do we need to disable preemption here?
>>     
> After thinking for a little while, you are theoretically right.
> In the current state, we could even be preempted between all operations
> ;-) Maybe after avi's suggestion of moving the call to it it will end up
> in a preempt safe region, but anyway, it's safer to add the preempt
> markers here.
> I'll put it in next version, thanks
>   
note that you cant call to kvm_write_guest with preemption disabled 
(witch you do few lines below)
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