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From: | Matthew Rosato |
Subject: | Re: [PATCH v2 1/3] vfio: Find DMA available capability |
Date: | Tue, 15 Sep 2020 09:39:20 -0400 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 |
On 9/15/20 2:14 AM, Philippe Mathieu-Daudé wrote:
Hi Matthew, On 9/15/20 12:29 AM, Matthew Rosato wrote:The underlying host may be limiting the number of outstanding DMA requests for type 1 IOMMU. Add helper functions to check for the DMA available capability and retrieve the current number of DMA mappings allowed. Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com> --- hw/vfio/common.c | 37 +++++++++++++++++++++++++++++++++++++ include/hw/vfio/vfio-common.h | 2 ++ 2 files changed, 39 insertions(+) diff --git a/hw/vfio/common.c b/hw/vfio/common.c index 3335714..7f4a338 100644 --- a/hw/vfio/common.c +++ b/hw/vfio/common.c @@ -844,6 +844,43 @@ vfio_get_region_info_cap(struct vfio_region_info *info, uint16_t id) return NULL; }+static struct vfio_info_cap_header *+vfio_get_iommu_type1_info_cap(struct vfio_iommu_type1_info *info, uint16_t id) +{ + struct vfio_info_cap_header *hdr; + void *ptr = info; + + if (!(info->flags & VFIO_IOMMU_INFO_CAPS)) { + return NULL; + } + + for (hdr = ptr + info->cap_offset; hdr != ptr; hdr = ptr + hdr->next) { + if (hdr->id == id) { + return hdr; + } + } + + return NULL; +} + +bool vfio_get_info_dma_avail(struct vfio_iommu_type1_info *info, + unsigned int *avail) +{ + struct vfio_info_cap_header *hdr; + struct vfio_iommu_type1_info_dma_avail *cap; + + /* If the capability cannot be found, assume no DMA limiting */ + hdr = vfio_get_iommu_type1_info_cap(info, + VFIO_IOMMU_TYPE1_INFO_DMA_AVAIL); + if (hdr == NULL || avail == NULL) {If you expect the caller to use avail=NULL, then why return false when there is available information?
I was not expecting the caller to use avail=NULL as there would be nowhere to stash the dma_avail count. But you're right, we can at least still know that the capability is enabled/disabled when avail=NULL.
I can change this by returning true/false solely based upon the existence of the capability (whether or not hdr==NULL) while only updating the caller's *avail value when avail!=NULL.
If that's no good, then the alternative would be an assert()
+ return false; + } + + cap = (void *) hdr; + *avail = cap->avail; + return true; +} + static int vfio_setup_region_sparse_mmaps(VFIORegion *region, struct vfio_region_info *info) { diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h index c78f3ff..661a380 100644 --- a/include/hw/vfio/vfio-common.h +++ b/include/hw/vfio/vfio-common.h @@ -178,6 +178,8 @@ VFIOGroup *vfio_get_group(int groupid, AddressSpace *as, Error **errp); void vfio_put_group(VFIOGroup *group); int vfio_get_device(VFIOGroup *group, const char *name, VFIODevice *vbasedev, Error **errp); +bool vfio_get_info_dma_avail(struct vfio_iommu_type1_info *info, + unsigned int *avail);extern const MemoryRegionOps vfio_region_ops;typedef QLIST_HEAD(VFIOGroupList, VFIOGroup) VFIOGroupList;
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