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

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Date:   Tue, 26 Apr 2022 21:51:18 +0200
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Juergen Gross <jgross@...e.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 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.

> 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.