s390x/pci: shrink DMA aperture to be bound by vfio DMA limit

Currently, s390x-pci performs accounting against the vfio DMA
limit and triggers the guest to clean up mappings when the limit
is reached. Let's go a step further and also limit the size of
the supported DMA aperture reported to the guest based upon the
initial vfio DMA limit reported for the container (if less than
than the size reported by the firmware/host zPCI layer).  This
avoids processing sections of the guest DMA table during global
refresh that, for common use cases, will never be used anway, and
makes exhausting the vfio DMA limit due to mismatch between guest
aperture size and host limit far less likely and more indicitive
of an error.

Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Message-Id: <20221028194758.204007-4-mjrosato@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

diff --git a/hw/s390x/s390-pci-vfio.c b/hw/s390x/s390-pci-vfio.c
index 5f0adb0b4aa5864aab8c67cbf87047b277ad81d4..f7bf36cec82d04e68ff50fe9b320a5dc552eef56 100644 (file)
--- a/hw/s390x/s390-pci-vfio.c
+++ b/hw/s390x/s390-pci-vfio.c
@@ -84,6 +84,7 @@ S390PCIDMACount *s390_pci_start_dma_count(S390pciState *s,
     cnt->users = 1;
     cnt->avail = avail;
     QTAILQ_INSERT_TAIL(&s->zpci_dma_limit, cnt, link);
+    pbdev->iommu->max_dma_limit = avail;
     return cnt;
 }
 
@@ -103,6 +104,7 @@ static void s390_pci_read_base(S390PCIBusDevice *pbdev,
     struct vfio_info_cap_header *hdr;
     struct vfio_device_info_cap_zpci_base *cap;
     VFIOPCIDevice *vpci =  container_of(pbdev->pdev, VFIOPCIDevice, pdev);
+    uint64_t vfio_size;
 
     hdr = vfio_get_device_info_cap(info, VFIO_DEVICE_INFO_CAP_ZPCI_BASE);
 
@@ -122,6 +124,15 @@ static void s390_pci_read_base(S390PCIBusDevice *pbdev,
     /* The following values remain 0 until we support other FMB formats */
     pbdev->zpci_fn.fmbl = 0;
     pbdev->zpci_fn.pft = 0;
+
+    /*
+     * If appropriate, reduce the size of the supported DMA aperture reported
+     * to the guest based upon the vfio DMA limit.
+     */
+    vfio_size = pbdev->iommu->max_dma_limit << TARGET_PAGE_BITS;
+    if (vfio_size < (cap->end_dma - cap->start_dma + 1)) {
+        pbdev->zpci_fn.edma = cap->start_dma + vfio_size - 1;
+    }
 }
 
 static bool get_host_fh(S390PCIBusDevice *pbdev, struct vfio_device_info *info,

diff --git a/include/hw/s390x/s390-pci-bus.h b/include/hw/s390x/s390-pci-bus.h
index 0605fcea24d313693e1b1a0491c8358edc3fe04c..1c46e3a2691c93abc1d89f9b89df156df8e69e76 100644 (file)
--- a/include/hw/s390x/s390-pci-bus.h
+++ b/include/hw/s390x/s390-pci-bus.h
@@ -278,6 +278,7 @@ struct S390PCIIOMMU {
     uint64_t g_iota;
     uint64_t pba;
     uint64_t pal;
+    uint64_t max_dma_limit;
     GHashTable *iotlb;
     S390PCIDMACount *dma_limit;
 };