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Re: [Qemu-devel] [PATCH qemu v14 16/18] spapr_iommu, vfio, memory: Notif

From: Alexey Kardashevskiy
Subject: Re: [Qemu-devel] [PATCH qemu v14 16/18] spapr_iommu, vfio, memory: Notify IOMMU about starting/stopping being used by VFIO
Date: Tue, 22 Mar 2016 17:24:33 +1100
User-agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.0

On 03/22/2016 03:45 PM, David Gibson wrote:
On Mon, Mar 21, 2016 at 06:47:04PM +1100, Alexey Kardashevskiy wrote:
The sPAPR TCE tables manage 2 copies when VFIO is using an IOMMU -
a guest view of the table and a hardware TCE table. If there is no VFIO
presense in the address space, then just the guest view is used, if
this is the case, it is allocated in the KVM. However since there is no
support yet for VFIO in KVM TCE hypercalls, when we start using VFIO,
we need to move the guest view from KVM to the userspace; and we need
to do this for every IOMMU on a bus with VFIO devices.

This adds vfio_start/vfio_stop callbacks in MemoryRegionIOMMUOps to
notifiy IOMMU about changing environment so it can reallocate the table
to/from KVM or (when available) hook the IOMMU groups with the logical
bus (LIOBN) in the KVM.

This removes explicit spapr_tce_set_need_vfio() call from PCI hotplug
path as the new callbacks do this better - they notify IOMMU at
the exact moment when the configuration is changed, and this also
includes the case of PCI hot unplug.

TODO: split into 2 or 3 patches, per maintainership area.

Signed-off-by: Alexey Kardashevskiy <address@hidden>

I'm finding this one much easier to follow than the previous revision.

  hw/ppc/spapr_iommu.c  | 12 ++++++++++++
  hw/ppc/spapr_pci.c    |  6 ------
  hw/vfio/common.c      |  9 +++++++++
  include/exec/memory.h |  4 ++++
  4 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/hw/ppc/spapr_iommu.c b/hw/ppc/spapr_iommu.c
index 6dc3c45..702075d 100644
--- a/hw/ppc/spapr_iommu.c
+++ b/hw/ppc/spapr_iommu.c
@@ -151,6 +151,16 @@ static uint64_t spapr_tce_get_page_sizes(MemoryRegion 
      return 1ULL << tcet->page_shift;

+static void spapr_tce_vfio_start(MemoryRegion *iommu)
+    spapr_tce_set_need_vfio(container_of(iommu, sPAPRTCETable, iommu), true);
+static void spapr_tce_vfio_stop(MemoryRegion *iommu)
+    spapr_tce_set_need_vfio(container_of(iommu, sPAPRTCETable, iommu), false);

Wonder if a single callback which takes a boolean might be a little
less clunky.

I have a feeling that at least once I was asked to do the opposite and now we have take_ownership/release_ownership. This does not seem to be much different and the existing names are more self-documenting than the previous vfio_notify() or whatever name I could think of.

  static void spapr_tce_table_do_enable(sPAPRTCETable *tcet);
  static void spapr_tce_table_do_disable(sPAPRTCETable *tcet);

@@ -211,6 +221,8 @@ static const VMStateDescription vmstate_spapr_tce_table = {
  static MemoryRegionIOMMUOps spapr_iommu_ops = {
      .translate = spapr_tce_translate_iommu,
      .get_page_sizes = spapr_tce_get_page_sizes,
+    .vfio_start = spapr_tce_vfio_start,
+    .vfio_stop = spapr_tce_vfio_stop,

  static int spapr_tce_table_realize(DeviceState *dev)
diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
index bfcafdf..af99a36 100644
--- a/hw/ppc/spapr_pci.c
+++ b/hw/ppc/spapr_pci.c
@@ -1121,12 +1121,6 @@ static void spapr_phb_add_pci_device(sPAPRDRConnector 
      void *fdt = NULL;
      int fdt_start_offset = 0, fdt_size;

-    if (object_dynamic_cast(OBJECT(pdev), "vfio-pci")) {
-        sPAPRTCETable *tcet = spapr_tce_find_by_liobn(phb->dma_liobn);
-        spapr_tce_set_need_vfio(tcet, true);
-    }
      if (dev->hotplugged) {
          fdt = create_device_tree(&fdt_size);
          fdt_start_offset = spapr_create_pci_child_dt(phb, pdev, fdt, 0);
diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index b257655..4e873b7 100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -421,6 +421,9 @@ static void vfio_listener_region_add(MemoryListener 
          QLIST_INSERT_HEAD(&container->giommu_list, giommu, giommu_next);

          memory_region_register_iommu_notifier(giommu->iommu, &giommu->n);
+        if (section->mr->iommu_ops && section->mr->iommu_ops->vfio_start) {
+            section->mr->iommu_ops->vfio_start(section->mr);
+        }
          memory_region_iommu_replay(giommu->iommu, &giommu->n,

@@ -466,6 +469,7 @@ static void vfio_listener_region_del(MemoryListener 
      VFIOContainer *container = container_of(listener, VFIOContainer, 
      hwaddr iova, end;
      int ret;
+    MemoryRegion *iommu = NULL;

      if (vfio_listener_skipped_section(section)) {
@@ -487,6 +491,7 @@ static void vfio_listener_region_del(MemoryListener 
          QLIST_FOREACH(giommu, &container->giommu_list, giommu_next) {
              if (giommu->iommu == section->mr) {
+                iommu = giommu->iommu;
                  QLIST_REMOVE(giommu, giommu_next);
@@ -519,6 +524,10 @@ static void vfio_listener_region_del(MemoryListener 
                       "0x%"HWADDR_PRIx") = %d (%m)",
                       container, iova, end - iova, ret);
+    if (iommu && iommu->iommu_ops && iommu->iommu_ops->vfio_stop) {
+        iommu->iommu_ops->vfio_stop(section->mr);
+    }

IIRC there can be multiple containers listening on the same PCI
address space.  In that case, this won't be correct, because once one
of the VFIO containers is removed, it will call vfio_stop, even though
the other VFIO container still needs the guest IOMMU to support it.

So I think you need some sort of refcounting here.

Right, missed this bit, good finding.


  static const MemoryListener vfio_memory_listener = {
diff --git a/include/exec/memory.h b/include/exec/memory.h
index eb5ce67..f1de133f 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -152,6 +152,10 @@ struct MemoryRegionIOMMUOps {
      IOMMUTLBEntry (*translate)(MemoryRegion *iommu, hwaddr addr, bool 
      /* Returns supported page sizes */
      uint64_t (*get_page_sizes)(MemoryRegion *iommu);
+    /* Called when VFIO starts using this */
+    void (*vfio_start)(MemoryRegion *iommu);
+    /* Called when VFIO stops using this */
+    void (*vfio_stop)(MemoryRegion *iommu);

  typedef struct CoalescedMemoryRange CoalescedMemoryRange;


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