Message-ID: <5088F176.5020108@de.ibm.com>
Date: Thu, 25 Oct 2012 09:59:50 +0200
From: Christian Borntraeger <borntraeger@de.ibm.com>
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To: Frederic Weisbecker <fweisbec@gmail.com>
CC: LKML <linux-kernel@vger.kernel.org>, Tony Luck <tony.luck@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Avi Kivity <avi@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>,
        Joerg Roedel <joerg.roedel@amd.com>, Alexander Graf <agraf@suse.de>,
        Xiantao Zhang <xiantao.zhang@intel.com>,
        Cornelia Huck <cornelia.huck@de.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Paul Gortmaker <paul.gortmaker@windriver.com>
Subject: Re: [PATCH 3/5] kvm: Directly account vtime to system on guest switch
References: <1351126313-17804-1-git-send-email-fweisbec@gmail.com> <1351126313-17804-4-git-send-email-fweisbec@gmail.com> <5088EF85.4080002@de.ibm.com> <CAFTL4hyFiE-G4VvmO+J2MMrJBFtH07ZcYp0GEnqoQ846_eivEQ@mail.gmail.com>
In-Reply-To: <CAFTL4hyFiE-G4VvmO+J2MMrJBFtH07ZcYp0GEnqoQ846_eivEQ@mail.gmail.com>
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On 25/10/12 09:56, Frederic Weisbecker wrote:
[...]
>>> * s390 doesn't disable irqs in its implementation of vtime_account().
>>> If vtime_account() in kvm races with an irq, the pending time might
>>> be accounted twice. With vtime_account_system_irqsafe() we are protected.
>>
>> We disable irqs before we call kvm_guest_enter/exit, see kvm-s390.c:
>>
>>
>> [...]
>>         if (!kvm_is_ucontrol(vcpu->kvm))
>>                 kvm_s390_deliver_pending_interrupts(vcpu);
>>         vcpu->arch.sie_block->icptcode = 0;
>>         local_irq_disable();
>>         kvm_guest_enter();
>>         local_irq_enable();
>> [...]
>>
> 
> Ah ok. Hmm I still need to keep it irqsafe for the other archs though,
> as it is currently with vtime_account(). So perhaps I can remove your
> local_irq_disable there and use vtime_account_system_irqsafe()
> instead?

Yes. We added the local_irq_disable code just for the vtime accounting.


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