linux-kernel - Re: [RESEND PATCH v2 0/6] vfio-pci: Add support for mmapping MSI-X table

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Date:	Wed, 8 Jun 2016 17:56:49 +0800
From:	Yongji Xie <xyjxie@...ux.vnet.ibm.com>
To:	Auger Eric <eric.auger@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, iommu@...ts.linux-foundation.org
Cc:	alex.williamson@...hat.com, bhelgaas@...gle.com, aik@...abs.ru,
	benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
	joro@...tes.org, warrier@...ux.vnet.ibm.com,
	zhong@...ux.vnet.ibm.com, nikunj@...ux.vnet.ibm.com,
	eric.auger@...aro.org, will.deacon@....com,
	gwshan@...ux.vnet.ibm.com, alistair@...ple.id.au,
	ruscur@...sell.cc, kevin.tian@...el.com, David.Laight@...LAB.COM
Subject: Re: [RESEND PATCH v2 0/6] vfio-pci: Add support for mmapping MSI-X
 table

Hi, Eric

On 2016/6/8 15:41, Auger Eric wrote:

> Hi Yongji,
>
> Le 02/06/2016 à 08:09, Yongji Xie a écrit :
>> Current vfio-pci implementation disallows to mmap the page
>> containing MSI-X table in case that users can write directly
>> to MSI-X table and generate an incorrect MSIs.
>>
>> However, this will cause some performance issue when there
>> are some critical device registers in the same page as the
>> MSI-X table. We have to handle the mmio access to these
>> registers in QEMU emulation rather than in guest.
>>
>> To solve this issue, this series allows to expose MSI-X table
>> to userspace when hardware enables the capability of interrupt
>> remapping which can ensure that a given PCI device can only
>> shoot the MSIs assigned for it. And we introduce a new bus_flags
>> PCI_BUS_FLAGS_MSI_REMAP to test this capability on PCI side
>> for different archs.
>>
>> The patch 3 are based on the proposed patchset[1].
> You may have noticed I sent a respin of [1] yesterday:
> http://www.gossamer-threads.com/lists/linux/kernel/2455187.
>
> Unfortunately you will see I removed the patch defining the new
> msi_domain_info MSI_FLAG_IRQ_REMAPPING flag you rely on in this series.
> I did so because I was not using it anymore. At the beginning this was
> used to detect whether the MSI assignment was safe but this
> method was covering cases where the MSI controller was
> upstream to the IOMMU. So now I rely on a mechanism where MSI controller
> are supposed to register their MSI doorbells and tag whether it is safe.
>
> I don't know yet how this change will be welcomed though. Depending
> on reviews/discussions, might happen we revert to the previous flag.
>
> If you need the feature you can embed the used patches in your series and
> follow the review process separately. Sorry for the setback.

Thanks for your notification. I'd better wait until your patches get
settled. Then I could exactly know which way we should use to test the
capability of interrupt remapping on ARM in my series.

Thanks,
Yongji