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Date: Tue, 15 Sep 2020 15:18:12 -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 v3] vfio iommu: Add dma available capability On 9/15/20 3:05 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 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. Link to latest QEMU patchset: https://lists.gnu.org/archive/html/qemu-devel/2020-09/msg05505.html > > 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(+) >
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