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Re: [PATCH 0/3] xen: remove some checks for always present Xen features
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Thu, 22 Apr 2021 17:28:36 +0200
- Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 22 Apr 2021 15:28:41 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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? Those are really just low
level additions I can't imagine will ever be removed again.
Juergen
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