linux-kernel - Re: [PATCH 0/2] KVM: async_pf: use_mm/mm

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Date:	Thu, 24 Apr 2014 16:55:45 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	Avi Kivity <avi.kivity@...il.com>, Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Dominik Dingel <dingel@...ux.vnet.ibm.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] KVM: async_pf: use_mm/mm_users fixes

On 04/24, Christian Borntraeger wrote:
>
> On 21/04/14 15:25, Oleg Nesterov wrote:
> > Hello.
> >
> > Completely untested and I know nothing about kvm ;) Please review.
> >
> > But use_mm() really looks misleading, and the usage of mm_users looks
> > "obviously wrong". I already sent this change while we were discussing
> > vmacache, but it was ignored. Since then kvm_async_page_present_sync()
> > was added into async_pf_execute() into async_pf_execute(), but it seems
> > to me that use_mm() is still unnecessary.
> >
> > Oleg.
> >
> >  virt/kvm/async_pf.c |   10 ++++------
> >  1 files changed, 4 insertions(+), 6 deletions(-)
> >
>
> I gave both patches some testing on s390, seems fine. I think patch2 really
> does fix a bug. So if Paolo, Marcelo, Gleb agree (maybe do a test on x86 for
> async_pf) both patches are good to go. Given that somebody tests this on x86:
>
> Acked-by: Christian Borntraeger <borntraeger@...ibm.com>

Thanks!

I think x86 should be fine, it doesn't select CONFIG_KVM_ASYNC_PF_SYNC and
get_user_pages() is certainly fine without use_mm(). And I still think it
should do get_user_pages(tsk => NULL) but this is minor.

Oleg.

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