From: Andrew Cooper <firstname.lastname@example.org>
To: Jan Beulich <email@example.com>, Juergen Gross <firstname.lastname@example.org>
Cc: Boris Ostrovsky <email@example.com>,
Stefano Stabellini <firstname.lastname@example.org>,
Thomas Gleixner <email@example.com>,
Ingo Molnar <firstname.lastname@example.org>, Borislav Petkov <email@example.com>,
"H. Peter Anvin" <firstname.lastname@example.org>,
Peter Zijlstra <email@example.com>,
Subject: Re: [PATCH 0/3] xen: remove some checks for always present Xen features
Date: Thu, 22 Apr 2021 16:51:27 +0100 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
On 22/04/2021 16:42, Jan Beulich wrote:
> On 22.04.2021 17:28, Juergen Gross wrote:
>> On 22.04.21 17:23, Jan Beulich wrote:
>>> On 22.04.2021 17:17, Juergen Gross wrote:
>>>> On 22.04.21 17:16, Jan Beulich wrote:
>>>>> On 22.04.2021 17:10, Juergen Gross wrote:
>>>>>> Some features of Xen can be assumed to be always present, so add a
>>>>>> central check to verify this being true and remove the other checks.
>>>>>> Juergen Gross (3):
>>>>>> xen: check required Xen features
>>>>>> xen: assume XENFEAT_mmu_pt_update_preserve_ad being set for pv guests
>>>>>> xen: assume XENFEAT_gnttab_map_avail_bits being set for pv guests
>>>>> I wonder whether it's a good idea to infer feature presence from
>>>>> version numbers. If (at some point in the past) you had inferred
>>>>> gnttab v2 being available by version, this would have been broken
>>>>> by its availability becoming controllable by a command line option
>>>>> in Xen.
>>>> I'm testing the feature to be really present when booting and issue a
>>>> message if it is not there.
>>> And how does this help if the feature really isn't there yet other code
>>> assumes it is?
>> Did you look at the features I'm testing?
> I did, yes.
>> Those are really just low
>> level additions I can't imagine will ever be removed again.
> I don't expect them to be removed. But I don't think the people having
> contributed gnttab v2 expected any such for it, either.
The trainwreck around gnttab v2 is a mistake I hope we're never going to
make again. I don't think it's a useful argument here.
The logic is fine. It's checking for the actual features in the ABI
upon which Linux depends.
Sure - someone could modify Xen to take the feature out, but they'd get
a red wall in CI as they break every Linux kernel released in the past
next prev parent reply other threads:[~2021-04-22 15:52 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-22 15:10 [PATCH 0/3] xen: remove some checks for always present Xen features Juergen Gross
2021-04-22 15:10 ` [PATCH 1/3] xen: check required " Juergen Gross
2021-04-22 15:26 ` Stefano Stabellini
2021-04-22 15:32 ` Juergen Gross
2021-05-10 12:11 ` Boris Ostrovsky
2021-05-10 13:21 ` Juergen Gross
2021-04-22 15:10 ` [PATCH 2/3] xen: assume XENFEAT_mmu_pt_update_preserve_ad being set for pv guests Juergen Gross
2021-04-22 15:10 ` [PATCH 3/3] xen: assume XENFEAT_gnttab_map_avail_bits " Juergen Gross
2021-04-22 15:16 ` [PATCH 0/3] xen: remove some checks for always present Xen features Jan Beulich
2021-04-22 15:17 ` Juergen Gross
2021-04-22 15:23 ` Jan Beulich
2021-04-22 15:28 ` Juergen Gross
2021-04-22 15:42 ` Jan Beulich
2021-04-22 15:49 ` Juergen Gross
2021-04-22 15:51 ` Andrew Cooper [this message]
2021-05-10 7:34 ` Juergen Gross
2021-05-10 11:31 ` Peter Zijlstra
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