linux-kernel - Re: [PATCH 5/5] vfio-pci: Allow to mmap MSI-X table if interrupt remapping is supported

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Message-ID: <f7d73ac3-470d-a0d2-0a97-05be630480dd@linux.vnet.ibm.com>
Date:	Tue, 3 May 2016 14:08:22 +0800
From:	Yongji Xie <xyjxie@...ux.vnet.ibm.com>
To:	"Tian, Kevin" <kevin.tian@...el.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Cc:	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"aik@...abs.ru" <aik@...abs.ru>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	"paulus@...ba.org" <paulus@...ba.org>,
	"mpe@...erman.id.au" <mpe@...erman.id.au>,
	"joro@...tes.org" <joro@...tes.org>,
	"warrier@...ux.vnet.ibm.com" <warrier@...ux.vnet.ibm.com>,
	"zhong@...ux.vnet.ibm.com" <zhong@...ux.vnet.ibm.com>,
	"nikunj@...ux.vnet.ibm.com" <nikunj@...ux.vnet.ibm.com>,
	"eric.auger@...aro.org" <eric.auger@...aro.org>,
	"will.deacon@....com" <will.deacon@....com>,
	"gwshan@...ux.vnet.ibm.com" <gwshan@...ux.vnet.ibm.com>,
	"David.Laight@...LAB.COM" <David.Laight@...LAB.COM>,
	"alistair@...ple.id.au" <alistair@...ple.id.au>,
	"ruscur@...sell.cc" <ruscur@...sell.cc>
Subject: Re: [PATCH 5/5] vfio-pci: Allow to mmap MSI-X table if interrupt
 remapping is supported

On 2016/5/3 13:34, Tian, Kevin wrote:

>> From: Yongji Xie
>> Sent: Wednesday, April 27, 2016 8:43 PM
>>
>> This patch enables mmapping MSI-X tables if hardware supports
>> interrupt remapping which can ensure that a given pci device
>> can only shoot the MSIs assigned for it.
>>
>> With MSI-X table mmapped, we also need to expose the
>> read/write interface which will be used to access MSI-X table.
>>
>> Signed-off-by: Yongji Xie <xyjxie@...ux.vnet.ibm.com>
> A curious question here. Does "allow to mmap MSI-X" essentially
> mean that KVM guest can directly read/write physical MSI-X
> structure then?
>
> Thanks
> Kevin
>

Here we just allow to mmap MSI-X table in kernel. It doesn't
mean all KVM guest can directly read/write physical MSI-X
structure. This should be decided by QEMU. For PPC64
platform, we would allow to passthrough the MSI-X table
because we know guest kernel would not write physical
MSI-X structure when enabling MSI.

Thanks,
Yongji