From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Julien Grall <julien@xen.org>, Jan Beulich <jbeulich@suse.com>,
<paul@xen.org>
Cc: "'Paul Durrant'" <pdurrant@amazon.com>,
"'Eslam Elnikety'" <elnikety@amazon.com>,
"'Ian Jackson'" <iwj@xenproject.org>, "'Wei Liu'" <wl@xen.org>,
"'Anthony PERARD'" <anthony.perard@citrix.com>,
"'George Dunlap'" <george.dunlap@citrix.com>,
"'Stefano Stabellini'" <sstabellini@kernel.org>,
"'Christian Lindig'" <christian.lindig@citrix.com>,
"'David Scott'" <dave@recoil.org>,
"'Volodymyr Babchuk'" <Volodymyr_Babchuk@epam.com>,
"'Roger Pau Monné'" <roger.pau@citrix.com>,
xen-devel@lists.xenproject.org
Subject: Re: [PATCH v5 1/4] domctl: introduce a new domain create flag, XEN_DOMCTL_CDF_evtchn_fifo, ...
Date: Fri, 4 Dec 2020 11:52:11 +0000 [thread overview]
Message-ID: <5de9f051-4071-4e09-528c-c1fb8345dc25@citrix.com> (raw)
In-Reply-To: <df1df316-9512-7b0c-fde1-aa4fc60ac70b@xen.org>
On 04/12/2020 11:45, Julien Grall wrote:
> Hi,
>
> I haven't looked at the series yet. Just adding some thoughts on why
> one would want such option.
>
> On 04/12/2020 09:43, Jan Beulich wrote:
>> On 04.12.2020 09:22, Paul Durrant wrote:
>>>> From: Jan Beulich <jbeulich@suse.com>
>>>> Sent: 04 December 2020 07:53
>>>>
>>>> On 03.12.2020 18:07, Paul Durrant wrote:
>>>>>> From: Jan Beulich <jbeulich@suse.com>
>>>>>> Sent: 03 December 2020 15:57
>>>>>>
>>>>>> ... this sound to me more like workarounds for buggy guests than
>>>>>> functionality the hypervisor _needs_ to have. (I can appreciate
>>>>>> the specific case here for the specific scenario you provide as
>>>>>> an exception.)
>>>>>
>>>>> If we want to have a hypervisor that can be used in a cloud
>>>>> environment
>>>>> then Xen absolutely needs this capability.
>>>>
>>>> As per above you can conclude that I'm still struggling to see the
>>>> "why" part here.
>>>>
>>>
>>> Imagine you are a customer. You boot your OS and everything is just
>>> fine... you run your workload and all is good. You then shut down
>>> your VM and re-start it. Now it starts to crash. Who are you going
>>> to blame? You did nothing to your OS or application s/w, so you are
>>> going to blame the cloud provider of course.
>>
>> That's a situation OSes are in all the time. Buggy applications may
>> stop working on newer OS versions. It's still the application that's
>> in need of updating then. I guess OSes may choose to work around
>> some very common applications' bugs, but I'd then wonder on what
>> basis "very common" gets established. I dislike the underlying
>> asymmetry / inconsistency (if not unfairness) of such a model,
>> despite seeing that there may be business reasons leading people to
>> think they want something like this.
>
> The discussion seems to be geared towards buggy guest so far. However,
> this is not the only reason that one my want to avoid exposing some
> features:
>
> 1) From the recent security issues (such as XSA-343), a knob to
> disable FIFO would be quite beneficials for vendors that don't need
> the feature.
>
> 2) Fleet management purpose. You may have a fleet with multiple
> versions of Xen. You don't want your customer to start relying on
> features that may not be available on all the hosts otherwise it
> complicates the guest placement.
>
> FAOD, I am sure there might be other features that need to be
> disabled. But we have to start somewhere :).
Absolutely top of the list, importance wise, is so we can test different
configurations, without needing to rebuild the hypervisor (and to a
lesser extent, without having to reboot).
It is a mistake that events/grants/etc were ever available unilaterally
in HVM guests. This is definitely a step in the right direction (but I
thought it would be too rude to ask Paul to make all of those CDF flags
at once).
~Andrew
next prev parent reply other threads:[~2020-12-04 11:52 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-03 12:41 [PATCH v5 0/4] Xen ABI feature control Paul Durrant
2020-12-03 12:41 ` [PATCH v5 1/4] domctl: introduce a new domain create flag, XEN_DOMCTL_CDF_evtchn_fifo, Paul Durrant
2020-12-03 15:22 ` Jan Beulich
2020-12-03 15:45 ` Paul Durrant
2020-12-03 15:56 ` Jan Beulich
2020-12-03 17:07 ` Paul Durrant
2020-12-03 17:19 ` Jürgen Groß
2020-12-03 18:44 ` Paul Durrant
2020-12-04 7:53 ` Jan Beulich
2020-12-04 8:22 ` Paul Durrant
2020-12-04 9:43 ` Jan Beulich
2020-12-04 11:45 ` Julien Grall
2020-12-04 11:52 ` Andrew Cooper [this message]
2020-12-04 17:41 ` Stefano Stabellini
2020-12-04 17:45 ` Andrew Cooper
2020-12-04 18:33 ` Durrant, Paul
2020-12-05 1:34 ` Stefano Stabellini
2020-12-07 9:17 ` Jan Beulich
2020-12-07 10:04 ` Julien Grall
2020-12-07 10:07 ` Julien Grall
2020-12-07 10:15 ` Jan Beulich
2020-12-07 10:23 ` Durrant, Paul
2020-12-03 12:41 ` [PATCH v5 2/4] domctl: introduce a new domain create flag, XEN_DOMCTL_CDF_evtchn_upcall, Paul Durrant
2020-12-03 12:41 ` [PATCH v5 3/4] libxl: introduce a 'libxl_xen_abi_features' enumeration Paul Durrant
2020-12-03 12:41 ` [PATCH v5 4/4] xl: introduce a 'xen-abi-features' option Paul Durrant
2020-12-03 13:15 ` [PATCH v5 0/4] Xen ABI feature control Jürgen Groß
2020-12-03 13:51 ` Paul Durrant
2020-12-03 13:58 ` Jürgen Groß
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