linux-kernel - Re: [PATCH V1 3/6] xen/virtio: Add option to restrict memory access under Xen

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Date:   Mon, 25 Apr 2022 09:47:49 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Oleksandr <olekstysh@...il.com>,
        Christoph Hellwig <hch@...radead.org>
Cc:     xen-devel@...ts.xenproject.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Julien Grall <julien@....org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH V1 3/6] xen/virtio: Add option to restrict memory access
 under Xen

On 24.04.22 18:53, Oleksandr wrote:
> 
> On 23.04.22 19:40, Christoph Hellwig wrote:
> 
> 
> Hello Christoph
> 
>> Please split this into one patch that creates grant-dma-ops, and another
>> that sets up the virtio restricted access helpers.
> 
> 
> Sounds reasonable, will do:
> 
> 1. grant-dma-ops.c with config XEN_GRANT_DMA_OPS
> 
> 2. arch_has_restricted_virtio_memory_access() with config XEN_VIRTIO
> 
> 
>>
>>> +
>>> +#ifdef CONFIG_ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS
>>> +int arch_has_restricted_virtio_memory_access(void)
>>> +{
>>> +    return (xen_has_restricted_virtio_memory_access() ||
>>> +            cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT));
>>> +}
>> So instead of hardcoding Xen here, this seems like a candidate for
>> another cc_platform_has flag.
> 
> 
> I have a limited knowledge of x86 and Xen on x86.
> 
> Would the Xen specific bits fit into Confidential Computing Platform checks? I 
> will let Juergen/Boris comment on this.

I don't think cc_platform_has would be correct here. Xen certainly
provides more isolation between guests and dom0, but "Confidential
Computing" is basically orthogonal to that feature.


Juergen

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