Re: [Qemu-devel] [PATCH qemu v6 07/15] vfio: spapr: Add SPAPR IOMMU v2 support (DMA memory preregistering)

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Apr 22, 2015 at 07:38:27PM +1000, Alexey Kardashevskiy wrote:
> On 04/22/2015 03:53 PM, David Gibson wrote:
> >On Sat, Apr 11, 2015 at 01:24:36AM +1000, Alexey Kardashevskiy wrote:
> >>This makes use of the new "memory registering" feature. The idea is
> >>to provide the userspace ability to notify the host kernel about pages
> >>which are going to be used for DMA. Having this information, the host
> >>kernel can pin them all once per user process, do locked pages
> >>accounting (once) and not spent time on doing that in real time with
> >>possible failures which cannot be handled nicely in some cases.
> >>
> >>This adds a guest RAM memory listener which notifies a VFIO container
> >>about memory which needs to be pinned/unpinned. VFIO MMIO regions
> >>(i.e. "skip dump" regions) are skipped.
> >>
> >>The feature is only enabled for SPAPR IOMMU v2. The host kernel changes
> >>are required. Since v2 does not need/support VFIO_IOMMU_ENABLE, this does
> >>not call it when v2 is detected and enabled.
> >>
> >>This does not change the guest visible interface.
> >>
> >>Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> >
> >Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> >
> >Albeit with some nits described below.

[snip]
> >>+    vfio_ram_do_region(container, section, VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY);
> >>+}
> >>+
> >>+static const MemoryListener vfio_spapr_ram_memory_listener = {
> >>+    .region_add = vfio_spapr_ram_listener_region_add,
> >>+    .region_del = vfio_spapr_ram_listener_region_del,
> >>+};
> >>+
> >>  static void vfio_spapr_listener_release(VFIOContainer *container)
> >>  {
> >>      memory_listener_unregister(&container->iommu_data.spapr.listener);
> >>  }
> >>
> >>-void spapr_memory_listener_register(VFIOContainer *container)
> >>+static void vfio_spapr_listener_release_v2(VFIOContainer *container)
> >>+{
> >>+    memory_listener_unregister(&container->iommu_data.spapr.listener);
> >>+    vfio_spapr_listener_release(container);
> >>+}
> >>+
> >>+int spapr_memory_listener_register(VFIOContainer *container, int ver)
> >>  {
> >>      container->iommu_data.spapr.listener = vfio_spapr_memory_listener;
> >>      container->iommu_data.release = vfio_spapr_listener_release;
> >>-
> >>      memory_listener_register(&container->iommu_data.spapr.listener,
> >>                               container->space->as);
> >>+    if (ver < 2) {
> >>+        return 0;
> >>+    }
> >
> >I wonder if it would make sense to store the IOMMU type value into the
> >VFIOContainer (from non-arch specific code).  It would avoid the
> >ad-hoc passing of version here and also allow for some sanity checks.
> 
> 
> What kind of checks? Cannot think of any which would make sense to do here
> and not in spapr_(pci|rtas)*.c

Well, all I was thinking of was something like
      assert(container->iommu_type == SPAPR_TCE_TYPE);
In spapr (or x86) callbacks from the core vfio code to make sure we
haven't somehow gotten here with a Type1 container.

> >>+
> >>+    container->iommu_data.spapr.ramlistener = vfio_spapr_ram_memory_listener;
> >>+    container->iommu_data.release = vfio_spapr_listener_release_v2;
> >>+    memory_listener_register(&container->iommu_data.spapr.ramlistener,
> >>+                             &address_space_memory);
> >>+
> >>+    container->iommu_data.spapr.ram_reg_initialized = true;
> >>+
> >>+    return container->iommu_data.spapr.ram_reg_error;
> >>  }
> >>diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> >>index d0b831c..b5ef446 100644
> >>--- a/include/hw/vfio/vfio-common.h
> >>+++ b/include/hw/vfio/vfio-common.h
> >>@@ -71,6 +71,9 @@ typedef struct VFIOType1 {
> >>
> >>  typedef struct VFIOSPAPR {
> >>      MemoryListener listener;
> >>+    MemoryListener ramlistener;
> >
> >The names "listener" and "ramlistener" don't exactly give a clear hint
> >as to what the difference between them is.  Maybe "register_listener"
> >for the new one since its purpose is to register dma memory.
> 
> 
> It is listening for RAM changes. If/when we decide to add something else to
> this listener, we won't have to change its name :) Still change?

Ah, I see.  I was forgetting that the other listener wasn't really
about RAM (I think an understandable error for a *Memory*Listener).

But actually I'm having trouble thinking of names that are clearly
better than the current ones.  So, I guess I don't really care.

> 
> 
> >I forget
> >what the purpose of the old one is, and so what a better name for it
> >might be.
> 
> It is listening on PHB address space for IOMMU table updates and translates
> those to MAP/UNMAP ioctls to VFIO containers.
> 
> 
> 
> >
> >>+    int ram_reg_error;
> >>+    bool ram_reg_initialized;
> >>  } VFIOSPAPR;
> >>
> >>  typedef struct VFIOContainer {
> >>@@ -156,6 +159,6 @@ extern int vfio_dma_unmap(VFIOContainer *container,
> >>                            hwaddr iova, ram_addr_t size);
> >>  bool vfio_listener_skipped_section(MemoryRegionSection *section);
> >>
> >>-extern void spapr_memory_listener_register(VFIOContainer *container);
> >>+extern int spapr_memory_listener_register(VFIOContainer *container, int ver);
> >>
> >>  #endif /* !HW_VFIO_VFIO_COMMON_H */
> >>diff --git a/trace-events b/trace-events
> >>index 1231ba4..2739140 100644
> >>--- a/trace-events
> >>+++ b/trace-events
> >>@@ -1563,6 +1563,7 @@ vfio_disconnect_container(int fd) "close container->fd=%d"
> >>  vfio_put_group(int fd) "close group->fd=%d"
> >>  vfio_get_device(const char * name, unsigned int flags, unsigned int num_regions, unsigned int num_irqs) "Device %s flags: %u, regions: %u, irqs: %u"
> >>  vfio_put_base_device(int fd) "close vdev->fd=%d"
> >>+vfio_ram_register(int req, uint64_t va, uint64_t size, int ret) "req=%d va=%"PRIx64" size=%"PRIx64" ret=%d"
> >>
> >>  #hw/acpi/memory_hotplug.c
> >>  mhp_acpi_invalid_slot_selected(uint32_t slot) "0x%"PRIx32
> >
> 
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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