linux-kernel - Re: [PATCH 2/2] virtio: replace arch_has_restricted_virtio_memory

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Date:   Wed, 27 Apr 2022 14:45:31 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Heiko Carstens <hca@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-arch@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-hyperv@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Arnd Bergmann <arnd@...db.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Oleksandr Tyshchenko <olekstysh@...il.com>
Subject: Re: [PATCH 2/2] virtio: replace
 arch_has_restricted_virtio_memory_access()

On 27.04.22 14:26, Borislav Petkov wrote:
> On Wed, Apr 27, 2022 at 08:40:08AM +0200, Juergen Gross wrote:
>> 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.
> 
> I'd say "never touch a running system" unless the platform features are
> of an advantage...

Depends on the use case IMHO.

All features being based on a cpuid bit are no candidates. Same applies
to all features used for alternative handling (assuming we don't want
to expand that to platform features).

I really have no idea whether this will leave any candidates. In case
it does, it might be interesting to switch those in order to save some
per-cpu bits.

Other candidates might be the x86_legacy_features.


Juergen

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