linux-kernel - Re: [PATCH] vfio iommu: Add dma limit capability

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Date:   Fri, 11 Sep 2020 13:03:41 -0400
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     alex.williamson@...hat.com, cohuck@...hat.com
Cc:     pmorel@...ux.ibm.com, schnelle@...ux.ibm.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfio iommu: Add dma limit capability

On 9/11/20 12:44 PM, Matthew Rosato wrote:
> Commit 492855939bdb ("vfio/type1: Limit DMA mappings per container") added
> a limit to the number of concurrent DMA requests for a vfio container.
> However, lazy unmapping in s390 can in fact cause quite a large number of
> outstanding DMA requests to build up prior to being purged, potentially
> the entire guest DMA space.  This results in unexpected 'VFIO_MAP_DMA
> failed: No space left on device' conditions seen in QEMU.
> 
> This patch proposes to provide the DMA limit via the VFIO_IOMMU_GET_INFO
> ioctl as a new capability.  A subsequent patchset to QEMU would collect
> this information and use it in s390 PCI support to tap the guest on the
> shoulder before overrunning the vfio limit.
> 

Link to the QEMU patchset:
https://lists.gnu.org/archive/html/qemu-devel/2020-09/msg04322.html

> Matthew Rosato (1):
>    vfio iommu: Add dma limit capability
> 
>   drivers/vfio/vfio_iommu_type1.c | 17 +++++++++++++++++
>   include/uapi/linux/vfio.h       | 16 ++++++++++++++++
>   2 files changed, 33 insertions(+)
>