From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Han, Huaitong" <huaitong.han@intel.com>
Subject: Re: [V3 PATCH 7/9] x86/hvm: pkeys,
 add pkeys support for guest_walk_tables
Date: Wed, 16 Dec 2015 09:03:38 +0000
Message-ID: <1450256625.4539.14.camel@intel.com>
References: <1449479780-19146-1-git-send-email-huaitong.han@intel.com>
	<1449479780-19146-8-git-send-email-huaitong.han@intel.com>
	<5669C23F.6080203@citrix.com>
	<566AA4D702000078000BE866@prv-mh.provo.novell.com>
	<1450167259.10563.9.camel@intel.com>
	<566FE51902000078000BF67A@prv-mh.provo.novell.com>
	<1450253821.4539.3.camel@intel.com>
	<56712FAB02000078000C004B@prv-mh.provo.novell.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xen.org>
In-Reply-To: <56712FAB02000078000C004B@prv-mh.provo.novell.com>
Content-Language: en-US
Content-ID: <74EDA4B1EF31EF44B65D90738DA0CB7A@intel.com>
List-Unsubscribe: <http://lists.xen.org/cgi-bin/mailman/options/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xen.org>
List-Help: <mailto:xen-devel-request@lists.xen.org?subject=help>
List-Subscribe: <http://lists.xen.org/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=subscribe>
Sender: xen-devel-bounces@lists.xen.org
Errors-To: xen-devel-bounces@lists.xen.org
To: "JBeulich@suse.com" <JBeulich@suse.com>, "andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>, "wei.liu2@citrix.com" <wei.liu2@citrix.com>, "ian.campbell@citrix.com" <ian.campbell@citrix.com>, "stefano.stabellini@eu.citrix.com" <stefano.stabellini@eu.citrix.com>, "george.dunlap@eu.citrix.com" <george.dunlap@eu.citrix.com>, "ian.jackson@eu.citrix.com" <ian.jackson@eu.citrix.com>, "george.dunlap@citrix.com" <george.dunlap@citrix.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>, "Nakajima,
	Jun" <jun.nakajima@intel.com>, "keir@xen.org" <keir@xen.org>
List-Id: xen-devel@lists.xenproject.org

On Wed, 2015-12-16 at 01:32 -0700, Jan Beulich wrote:
> > > > On 16.12.15 at 09:16, <huaitong.han@intel.com> wrote:
> > On Tue, 2015-12-15 at 02:02 -0700, Jan Beulich wrote:
> > > Well, I wouldn't want you to introduce a brand new function, but
> > > instead just factor out the necessary piece from xsave() (making
> > > the new one take a struct xsave_struct * instead of a struct vcpu
> > > *,
> > > and calling it from what is now xsave()).
> > So the function looks like this:
> > unsigned int get_xsave_pkru(struct vcpu *v)
> > {
> >     void *offset;
> >     struct xsave_struct *xsave_area;
> >     uint64_t mask = XSTATE_PKRU;
> >     unsigned int index = fls64(mask) - 1;
> >     unsigned int pkru = 0;
> > 
> >     if ( !cpu_has_xsave )
> >         return 0;
> >     
> >     BUG_ON(xsave_cntxt_size < XSTATE_AREA_MIN_SIZE);
> >     xsave_area = _xzalloc(xsave_cntxt_size, 64);
> >     if ( xsave_area == NULL )
> >         return 0;
> > 
> >     xsave(xsave_area, mask);
> >     offset = (void *)xsave_area + (xsave_area_compressed(xsave) ? 
> >             XSTATE_AREA_MIN_SIZE : xstate_offsets[index] );
> >     memcpy(&pkru, offset, sizeof(pkru));
> > 
> >     xfree(xsave_area);
> > 
> >     return pkru;
> > }
> 
> Depending on how frequently this might get called, the allocation
> overhead may not be tolerable. I.e. you may want to set up e.g.
> a per-CPU buffer up front. Or you check whether using RDPKRU
> (with temporarily setting CR4.PKE) is cheaper than what you
> do right now.
RDPKRU does cost less than the function, and if temporarily setting
CR4.PKE is accepted, I will use RDPKRU instead of the function.

Andrew, what is your opinion?