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

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Date:   Wed, 27 Apr 2022 14:28:44 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Juergen Gross <jgross@...e.com>,
        Tom Lendacky <thomas.lendacky@....com>
Cc:     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>,
        Heiko Carstens <hca@...ux.ibm.com>,
        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 Wed, Apr 27, 2022 at 08:37:31AM +0200, Juergen Gross wrote:
> On 26.04.22 19:35, 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.
> 
> Okay, fine with me.
> 
> > 
> > > diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> > > index b43bc24d2bb6..6043ba6cd17d 100644
> > > --- a/arch/x86/mm/mem_encrypt_identity.c
> > > +++ b/arch/x86/mm/mem_encrypt_identity.c
> > > @@ -40,6 +40,7 @@
> > >   #include <linux/mm.h>
> > >   #include <linux/mem_encrypt.h>
> > >   #include <linux/cc_platform.h>
> > > +#include <linux/platform-feature.h>
> > >   #include <asm/setup.h>
> > >   #include <asm/sections.h>
> > > @@ -566,6 +567,10 @@ void __init sme_enable(struct boot_params *bp)
> > >   	} else {
> > >   		/* SEV state cannot be controlled by a command line option */
> > >   		sme_me_mask = me_mask;
> > > +
> > > +		/* Set restricted memory access for virtio. */
> > > +		platform_set_feature(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
> > 
> > Huh, what does that have to do with SME?
> 
> I picked the function where sev_status is being set, as this seemed to be
> the correct place to set the feature bit.

What I don't understand is what does restricted memory access have to do
with AMD SEV and how does play together with what you guys are trying to
do?

The big picture pls.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette