Re: [PATCH 1/2] kernel: add platform_has() infrastructure

From: Juergen Gross via Virtualization <virtualization@lists.linux-foundation.org>
To: Borislav Petkov <bp@alien8.de>
Cc: linux-hyperv@vger.kernel.org,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	virtualization@lists.linux-foundation.org,
	"H. Peter Anvin" <hpa@zytor.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	linux-arch@vger.kernel.org, linux-s390@vger.kernel.org,
	Wei Liu <wei.liu@kernel.org>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Arnd Bergmann <arnd@arndb.de>,
	x86@kernel.org, Dexuan Cui <decui@microsoft.com>,
	Christoph Hellwig <hch@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Heiko Carstens <hca@linux.ibm.com>,
	Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org,
	Oleksandr Tyshchenko <olekstysh@gmail.com>,
	Sven Schnelle <svens@linux.ibm.com>
Subject: Re: [PATCH 1/2] kernel: add platform_has() infrastructure
Date: Wed, 27 Apr 2022 08:20:54 +0200	[thread overview]
Message-ID: <f7dca1db-8e4f-a793-231b-a69423451463@suse.com> (raw)
In-Reply-To: <YmgsYvWQchxub8cW@zn.tnic>

[-- Attachment #1.1.1.1: Type: text/plain, Size: 1053 bytes --]

On 26.04.22 19:31, Borislav Petkov wrote:
> On Tue, Apr 26, 2022 at 03:40:20PM +0200, Juergen Gross wrote:
>> diff --git a/kernel/platform-feature.c b/kernel/platform-feature.c
>> new file mode 100644
>> index 000000000000..2d52f8442cd5
>> --- /dev/null
>> +++ b/kernel/platform-feature.c
>> @@ -0,0 +1,7 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +
>> +#include <linux/cache.h>
>> +#include <linux/platform-feature.h>
>> +
>> +unsigned long __read_mostly platform_features[PLATFORM_FEAT_ARRAY_SZ];
> 
> Probably __ro_after_init.

Yes, good idea.

> 
>> +EXPORT_SYMBOL_GPL(platform_features);
> 
> You probably should make that thing static and use only accessors to
> modify it in case you wanna change the underlying data structure in the
> future.

The question is whether we think that those platform features will be used
in hot paths or not. If so the inline accessors (at least the platform_has()
one) would be preferred IMO.

OTOH really performance critical cases could use static_branch or such.

Juergen

[-- Attachment #1.1.1.2: OpenPGP public key --]
[-- Type: application/pgp-keys, Size: 3149 bytes --]

[-- Attachment #1.2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 495 bytes --]

[-- Attachment #2: Type: text/plain, Size: 183 bytes --]

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization