qemu-kvm/kvm-s390x-pci-shrink-DMA-aperture-to-be-bound-by-vfio-DM.patch

From a0b6c21b555566eb6bc38643269d14c82dfd0226 Mon Sep 17 00:00:00 2001
From: Matthew Rosato <mjrosato@linux.ibm.com>
Date: Fri, 28 Oct 2022 15:47:58 -0400
Subject: [PATCH 10/11] s390x/pci: shrink DMA aperture to be bound by vfio DMA
 limit
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RH-Author: Cédric Le Goater <clg@redhat.com>
RH-MergeRequest: 250: s390x/pci: reset ISM passthrough devices on shutdown and system reset
RH-Bugzilla: 2163713
RH-Acked-by: Thomas Huth <thuth@redhat.com>
RH-Acked-by: Cornelia Huck <cohuck@redhat.com>
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
RH-Commit: [3/4] aa241dd250ad5e696b67c87dddc31ee5aaee9c0e

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>
(cherry picked from commit df202e3ff3fccb49868e08f20d0bda86cb953fbe)
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
 hw/s390x/s390-pci-vfio.c        | 11 +++++++++++
 include/hw/s390x/s390-pci-bus.h |  1 +
 2 files changed, 12 insertions(+)

diff --git a/hw/s390x/s390-pci-vfio.c b/hw/s390x/s390-pci-vfio.c
index 2aefa508a0..99806e2a84 100644
--- 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 0605fcea24..1c46e3a269 100644
--- 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;
 };
-- 
2.37.3