From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm
 async_pf_execute()
Date: Mon, 28 Apr 2014 17:31:22 +0200
Message-ID: <535E744A.1060708@redhat.com>
References: <20140421132558.GA13608@redhat.com> <5356CDDF.5000203@de.ibm.com> <5356DA2F.8080606@de.ibm.com> <20140423193228.GA3441@redhat.com> <20140428140602.GC10488@redhat.com>
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Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
	Avi Kivity <avi.kivity@gmail.com>,
	Gleb Natapov <gleb@kernel.org>,
	Dominik Dingel <dingel@linux.vnet.ibm.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
To: Andrea Arcangeli <aarcange@redhat.com>,
	Oleg Nesterov <oleg@redhat.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20140428140602.GC10488@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

Il 28/04/2014 16:06, Andrea Arcangeli ha scritto:
>> >
>> > "task" is only used to increment task_struct->xxx_flt. I don't think
>> > async_pf_execute() actually needs this (current is PF_WQ_WORKER after
>> > all), but I didn't dare to do another change in the code I can hardly
>> > understand.
> Considering the faults would be randomly distributed among the kworker
> threads my preference would also be for NULL instead of current.
>
> ptrace and uprobes tends to be the only two places that look into
> other mm with gup, ptrace knows the exact pid that it is triggering
> the fault into, so it also can specify the correct task so the fault
> goes in the right task struct. uprobes uses NULL.

KVM knows the correct task (it was in current when kvm_create_vm was 
called), and doing accounting right would be nice.  But I agree that 
NULL is less misleading than a dummy current, and I applied patch 3 too.

Paolo