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From: Jan Beulich <jbeulich@suse.com>
To: Juergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	xen-devel@lists.xenproject.org
Subject: Re: [PATCH 0/3] xen: remove some checks for always present Xen features
Date: Thu, 22 Apr 2021 17:23:53 +0200	[thread overview]
Message-ID: <08e3fcf1-dabc-c550-f76c-47a78a12274b@suse.com> (raw)
In-Reply-To: <b69df7d3-6fcb-a565-9ec5-a272b6163320@suse.com>

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?

Jan


  reply	other threads:[~2021-04-22 15:24 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-22 15:10 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 [this message]
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
2021-05-10  7:34 ` Juergen Gross
2021-05-10 11:31   ` Peter Zijlstra

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