Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v4 11/15] pci: Add pci_iomap_shared{,_range}
To:     "Michael S. Tsirkin" <mst@redhat.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@google.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        linux-pci@vger.kernel.org, linux-alpha@vger.kernel.org,
        linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org,
        sparclinux@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-doc@vger.kernel.org,
        virtualization@lists.linux-foundation.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>
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>
Message-ID: <26a3cce5-ddf7-cbe6-a41e-58a2aea48f78@linux.intel.com>
Date:   Mon, 23 Aug 2021 17:30:54 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Firefox/78.0 Thunderbird/78.11.0
MIME-Version: 1.0
In-Reply-To: <20210823195409-mutt-send-email-mst@kernel.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk


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.

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer