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

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Date:	Fri, 13 May 2016 02:36:27 +0000
From:	"Tian, Kevin" <kevin.tian@...el.com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	Yongji Xie <xyjxie@...ux.vnet.ibm.com>,
	David Laight <David.Laight@...LAB.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>,
	"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>,
	"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

> From: Tian, Kevin
> Sent: Friday, May 13, 2016 10:33 AM
> 
> > means.  The MSI-X vector table of a device is always considered
> > untrusted which is why we require user opt-ins to subvert that
> > protection.  Thanks,
> >
> 
> I only partially agree with this statement since there is different
> trust level for kernel space driver and user space driver.
> 
> OS may choose to trust kernel space driver then it can enable IRQ
> remapping only for load balance purpose w/o source id verfification.
> In such case MSI-X vector table is trusted and fully under kernel
> control. Allowing to mmap MSI-X table in user space definitely
> breaks that boundary.
> 
> Anyway my point is simple. Let's ignore how Linux kernel implements
> IRQ remapping on x86 (which may change time to time), and just
> focus on architectural possibility. Non-x86 platform may implement
> IRQ remapping completely separate from device side, then checking
> availability of IRQ remapping is enough to decide whether mmap
> MSI-X table is safe. x86 with VT-d can be configured to a mode
> requiring host control of both MSI-X entry and IRQ remapping hardware
> (without source id check). In such case it's insufficient to make
> decision simply based on IRQ remapping availability. We need a way
> to query from IRQ remapping module whether it's actually safe to
> mmap MSI-X.
> 

Or another way is to have VFIO explicitly request intel-iommu to
enforce sid check when IRQ remapping is enabled...

Thanks
Kevin