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From:   Matthew Rosato <mjrosato@linux.ibm.com>
To:     alex.williamson@redhat.com, cohuck@redhat.com
Cc:     pmorel@linux.ibm.com, schnelle@linux.ibm.com, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH v3] vfio iommu: Add dma available capability
Date:   Tue, 15 Sep 2020 15:05:17 -0400
Message-Id: <1600196718-23238-1-git-send-email-mjrosato@linux.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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 remaining number of allowable DMA 
requests 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.

Changes from v2:
- Typos / fixed stale comment block

Matthew Rosato (1):
  vfio iommu: Add dma available capability

 drivers/vfio/vfio_iommu_type1.c | 17 +++++++++++++++++
 include/uapi/linux/vfio.h       | 15 +++++++++++++++
 2 files changed, 32 insertions(+)

-- 
1.8.3.1