From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH v4 11/15] pci: Add pci_iomap_shared{,_range}
Date: Tue, 24 Aug 2021 05:12:03 -0400
Message-ID: <20210824050842-mutt-send-email-mst@kernel.org>
References: <20210805005218.2912076-1-sathyanarayanan.kuppuswamy@linux.intel.com>
 <20210805005218.2912076-12-sathyanarayanan.kuppuswamy@linux.intel.com>
 <20210823195409-mutt-send-email-mst@kernel.org>
 <26a3cce5-ddf7-cbe6-a41e-58a2aea48f78@linux.intel.com>
Mime-Version: 1.0
Return-path: <sparclinux-owner@vger.kernel.org>
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;
        s=mimecast20190719; t=1629796332;
        h=from:from:reply-to:subject:subject:date:date:message-id:message-id:
         to:to:cc:cc:mime-version:mime-version:content-type:content-type:
         in-reply-to:in-reply-to:references:references;
        bh=UO2zBbBs1G6uT3R3xch5pdAd9JzMFmQCenqYTZnnAws=;
        b=ciI55oT+4ry/YlJLlDbugRTfprdq8vmV8TxkKb01viiPuKkCGhO804W14LS76wuqUuE+pJ
        KfuZCRH8vytOEwSgN/ZVJOTN8ffYpvEEqlTWk9AnsTrzYcdsb0W9dwj/0mW756MhXE+X9y
        cur4x82RiyCts6/Ze32mfLqL6/9yMes=
Content-Disposition: inline
In-Reply-To: <26a3cce5-ddf7-cbe6-a41e-58a2aea48f78@linux.intel.com>
List-ID: <linux-alpha.vger.kernel.org>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
To: "Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Peter Zijlstra <peterz@infradead.org>, Andy Lutomirski <luto@kernel.org>, Bjorn Helgaas <bhelgaas@google.com>, Richard Henderson <rth@twiddle.net>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>, James E J Bottomley <James.Bottomley@hansenpartnership.com>, Helge Deller <deller@gmx.de>, "David S . Miller" <davem@davemloft.net>, Arnd Bergmann <arnd@arndb.de>, Jonathan Corbet <corbet@lwn.net>, Peter H Anvin <hpa@zytor.com>, Dave Hansen <dave.hansen@intel.com>, Tony Luck <tony.luck@intel.com>, Dan Williams <dan.j.williams@intel.com>, Andi Kleen <ak@linux.intel.com>, Kirill Shutemov <kirill.shutemov@linux.intel.com>, Sean Christopherson <seanjc@g>

On Mon, Aug 23, 2021 at 05:30:54PM -0700, Kuppuswamy, Sathyanarayanan wrote:
> 
> 
> On 8/23/21 4:56 PM, Michael S. Tsirkin wrote:
> > > Add a new variant of pci_iomap for mapping all PCI resources
> > > of a devices as shared memory with a hypervisor in a confidential
> > > guest.
> > > 
> > > Signed-off-by: Andi Kleen<ak@linux.intel.com>
> > > Signed-off-by: Kuppuswamy Sathyanarayanan<sathyanarayanan.kuppuswamy@linux.intel.com>
> > I'm a bit puzzled by this part. So why should the guest*not*  map
> > pci memory as shared? And if the answer is never (as it seems to be)
> > then why not just make regular pci_iomap DTRT?
> 
> It is in the context of confidential guest (where VMM is un-trusted). So
> we don't want to make all PCI resource as shared. It should be allowed
> only for hardened drivers/devices.

I can't say this answers the question at all. PCI devices are part of
the VMM and so un-trusted. In particular PCI devices do not have
the key to decrypt memory. Therefore as far as I can see PCI resources
should not be encrypted.  I conclude they all should be marked
shared.

If I'm wrong can you please give an example of a PCI resource
that is encrypted?

-- 
MST