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

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Date:   Tue, 26 Apr 2022 19:35:43 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Juergen Gross <jgross@...e.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 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.

> 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?

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.

Thx.

-- 
Regards/Gruss,
    Boris.

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