linux-kernel - Re: [PATCH v2 6/7] kvm,x86: RCU based table free

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Date:	Tue, 5 Jun 2012 14:21:50 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"mtosatti@...hat.com" <mtosatti@...hat.com>,
	"avi@...hat.com" <avi@...hat.com>,
	"raghukt@...ux.vnet.ibm.com" <raghukt@...ux.vnet.ibm.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"jeremy@...p.org" <jeremy@...p.org>,
	"vatsa@...ux.vnet.ibm.com" <vatsa@...ux.vnet.ibm.com>,
	"hpa@...or.com" <hpa@...or.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH v2 6/7] kvm,x86: RCU based table free

On Tue, 5 Jun 2012, Nikunj A Dadhania wrote:
> On Tue, 5 Jun 2012 12:58:32 +0100, Stefano Stabellini <stefano.stabellini@...citrix.com> wrote:
> > On Tue, 5 Jun 2012, Nikunj A Dadhania wrote:
> > > On Tue, 5 Jun 2012 11:48:02 +0100, Stefano Stabellini <stefano.stabellini@...citrix.com> wrote:
> > > > 
> > > > I am also interested in introducing HAVE_RCU_TABLE_FREE on x86 for Xen.
> > > > Maybe we can pull our efforts together :-)
> > > > 
> > > > Giving a look at this patch, it doesn't look like it is introducing
> > > > CONFIG_HAVE_RCU_TABLE_FREE anywhere under arch/x86.
> > > > How is the user supposed to set it?
> > > >
> > > I am doing that in the next patch only for KVM-ParavirtTLB flush, as
> > > there is a bug in this implementation that patch [7/7] fixes.
> > > 
> > > Refer following thread for details:
> > > http://mid.gmane.org/1337254086.4281.26.camel@twins
> > > http://mid.gmane.org/1337273959.4281.62.camel@twins
> > 
> > Thanks, somehow I missed the 7/7 patch.
> > 
> > From the Xen POV, your patch is fine because we'll just select
> > PARAVIRT_TLB_FLUSH on CONFIG_XEN (see appended patch for completeness).
> > 
> Selecting ARCH_HW_WALKS_PAGE_TABLE in place of PARAVIRT_TLB_FLUSH should
> suffice.

We would also need to select HAVE_RCU_TABLE_FREE, but it could be a good
idea, not go through PARAVIRT_TLB_FLUSH.

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