From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: PML (Page Modification Logging) design for Xen Date: Wed, 11 Mar 2015 11:11:42 +0000 Message-ID: <550022EE.8060302@citrix.com> References: <54DB129D.3060102@linux.intel.com> <54DB4294.1080406@citrix.com> <54DC1249.60507@linux.intel.com> <54E323C7020000780006089B@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: George Dunlap , Jan Beulich Cc: Kai Huang , Keir Fraser , "Tian, Kevin" , Tim Deegan , "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org On 11/03/15 10:59, George Dunlap wrote: > On Tue, Feb 17, 2015 at 10:19 AM, Jan Beulich wrote: >>>>> On 12.02.15 at 03:39, wrote: >>> On 02/11/2015 07:52 PM, Andrew Cooper wrote: >>>> On 11/02/15 08:28, Kai Huang wrote: >>>>> Design >>>>> ====== >>>>> >>>>> - PML feature is used globally >>>>> >>>>> A new Xen boot parameter, say 'opt_enable_pml', will be introduced to >>>>> control PML feature detection, and PML feature will only be detected >>>>> if opt_enable_pml = 1. Once PML feature is detected, it will be used >>>>> for dirty logging for all domains globally. Currently we don't support >>>>> to use PML on basis of per-domain as it will require additional >>>>> control from XL tool. >>>> Rather than adding in a new top level command line option for an ept >>>> subfeature, it would be preferable to add an "ept=" option which has >>>> "pml" as a sub boolean. >>> Which is good to me, if Jan agrees. >>> >>> Jan, which do you prefer here? >> A single "ept=" option as Andrew suggested. > Sorry to be coming late to this party -- what's the logic behind > having this enabled with "ept="? You're not changing anything about > how EPT itself works; you're adding a secondary feature which happens > to depend on ept. Is there another hypervisor command-line option you > had in mind that works this way? iommu= > > It might also be nice to be able to enable or disable this feature > with a sysctl call; but that's just a nice-to-have. This feature should either be used or not. It is impractical to enable/disable at runtime. However, it absolutely wants a knob for tweaking. The likely consequence of a bug in the implementation is VM memory corruption on migrate, and you can get away with missing a large amount of a domains memory before it blows up noticeably. ~Andrew