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From: George Dunlap <george.dunlap@citrix.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Andrew Cooper <Andrew.Cooper3@citrix.com>,
	"Tim \(Xen.org\)" <tim@xen.org>,
	Julien Grall <julien.grall@arm.com>,
	Paul Durrant <Paul.Durrant@citrix.com>,
	Jan Beulich <jbeulich@suse.com>,
	Ian Jackson <Ian.Jackson@citrix.com>,
	Anthony Perard <anthony.perard@citrix.com>,
	Xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [Xen-devel] [PATCH] x86/libxl: choose a sane default for HAP
Date: Thu, 5 Sep 2019 12:44:16 +0100	[thread overview]
Message-ID: <f198f4e9-4c67-73ad-1279-2b2b01f3d456@citrix.com> (raw)
In-Reply-To: <20190905110127.t3y2lqxzvlhjgfhl@Air-de-Roger>

On 9/5/19 12:01 PM, Roger Pau Monné wrote:
> On Thu, Sep 05, 2019 at 12:34:11PM +0200, George Dunlap wrote:
>>
>>
>>> On Sep 5, 2019, at 11:01 AM, Roger Pau Monne <roger.pau@citrix.com> wrote:
>>>
>>> On Thu, Sep 05, 2019 at 11:52:59AM +0200, Jan Beulich wrote:
>>>> On 05.09.2019 11:34, Roger Pau Monne wrote:
>>>>> Current libxl code will always enable Hardware Assisted Paging (HAP),
>>>>> expecting that the hypervisor will fallback to shadow if HAP is not
>>>>> available. With the changes to the domain builder that's not the case
>>>>> any longer, and the hypervisor will raise an error if HAP is not
>>>>> available instead of silently falling back to shadow.
>>>>
>>>> Would it really be much more involved than the change here to restore
>>>> silent defaulting to shadow?
>>>
>>> But that would mean that a user having selected hap=1 on the config
>>> file would get silently defaulted to shadow, which is wrong IMO.
>>
>> At the libxl layer, aren’t the options tristate?  I.e., this would be “hap”, “shadow”, or “not specified”?
>>
>> The user needs to be able to specify “always use shadow”, “always use HAP”, or “use HAP if available, otherwise use shadow”.
> 
> The "use HAP if available, otherwise use shadow" is currently only
> possibly expressed by not setting the hap option in the config file.
> 
>> At the moment, leaving it empty should be “use HAP if available, otherwise use shadow”; so “hap = 1” should fail if HAP is not available.
> 
> Right, this is what this patch is trying to accomplish.

Right; I wasn't trying to contradict you so much as "weigh in" (and
basically agree with you).

 -George

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      reply	other threads:[~2019-09-05 11:44 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-05  9:34 [Xen-devel] [PATCH] x86/libxl: choose a sane default for HAP Roger Pau Monne
2019-09-05  9:40 ` Paul Durrant
2019-09-05  9:57   ` Roger Pau Monné
2019-09-05  9:52 ` Jan Beulich
2019-09-05 10:00   ` Andrew Cooper
2019-09-05 10:01   ` Roger Pau Monné
2019-09-05 10:32     ` Jan Beulich
2019-09-05 10:34       ` Andrew Cooper
2019-09-05 10:34     ` George Dunlap
2019-09-05 11:01       ` Roger Pau Monné
2019-09-05 11:44         ` George Dunlap [this message]

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