linux-kernel - Re: [PATCH 0/3] xen: remove some checks for always present Xen features

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Message-ID: <df27aba6-c67e-d66e-f00e-75a1f76de921@suse.com>
Date:   Thu, 22 Apr 2021 17:16:03 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 0/3] xen: remove some checks for always present Xen
 features

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.

Jan