Re: [PATCH 2/2] virtio: replace arch_has_restricted_virtio_memory_access()

From: Juergen Gross <jgross@suse.com>
To: Heiko Carstens <hca@linux.ibm.com>, Borislav Petkov <bp@alien8.de>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
	linux-arch@vger.kernel.org, linux-s390@vger.kernel.org,
	linux-hyperv@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	Arnd Bergmann <arnd@arndb.de>, Vasily Gorbik <gor@linux.ibm.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	Christian Borntraeger <borntraeger@linux.ibm.com>,
	Sven Schnelle <svens@linux.ibm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Jason Wang <jasowang@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	Oleksandr Tyshchenko <olekstysh@gmail.com>
Subject: Re: [PATCH 2/2] virtio: replace arch_has_restricted_virtio_memory_access()
Date: Wed, 27 Apr 2022 08:40:08 +0200	[thread overview]
Message-ID: <49e33b14-b439-340b-aa59-a6c77daa4929@suse.com> (raw)
In-Reply-To: <YmhNNrLW+tM2gnZB@osiris>

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On 26.04.22 21:51, Heiko Carstens wrote:
> On Tue, Apr 26, 2022 at 07:35:43PM +0200, Borislav Petkov wrote:
>> On Tue, Apr 26, 2022 at 03:40:21PM +0200, Juergen Gross wrote:
>>>   /* protected virtualization */
>>>   static void pv_init(void)
>>>   {
>>>   	if (!is_prot_virt_guest())
>>>   		return;
>>>   
>>> +	platform_set_feature(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
>>
>> Kinda long-ish for my taste. I'll probably call it:
>>
>> 	platform_set()
>>
>> as it is implicit that it sets a feature bit.
> 
> ...and platform_clear(), instead of platform_reset_feature() please.

Fine with me.

> 
>> In any case, yeah, looks ok at a quick glance. It would obviously need
>> for more people to look at it and say whether it makes sense to them and
>> whether that's fine to have in generic code but so far, the experience
>> with cc_platform_* says that it seems to work ok in generic code.
> 
> We _could_ convert s390's machine flags to this mechanism. Those flags
> are historically per-cpu, but if I'm not mistaken none of them is
> performance critical anymore, and those who are could/should probably
> transformed to jump labels or alternatives anyway.

I was planning to look at the x86 cpu features to see whether some of
those might be candidates to be switched to platform features instead.

Juergen

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