Re: [Qemu-devel] [PATCH qemu v14 17/18] vfio/spapr: Use VFIO_SPAPR_TCE_v2_IOMMU

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

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On Wed, Mar 23, 2016 at 01:12:59PM +1100, Alexey Kardashevskiy wrote:
> On 03/23/2016 12:08 PM, David Gibson wrote:
> >On Tue, Mar 22, 2016 at 04:54:07PM +1100, Alexey Kardashevskiy wrote:
> >>On 03/22/2016 04:14 PM, David Gibson wrote:
> >>>On Mon, Mar 21, 2016 at 06:47:05PM +1100, Alexey Kardashevskiy wrote:
> >>>>New VFIO_SPAPR_TCE_v2_IOMMU type supports dynamic DMA window management.
> >>>>This adds ability to VFIO common code to dynamically allocate/remove
> >>>>DMA windows in the host kernel when new VFIO container is added/removed.
> >>>>
> >>>>This adds VFIO_IOMMU_SPAPR_TCE_CREATE ioctl to vfio_listener_region_add
> >>>>and adds just created IOMMU into the host IOMMU list; the opposite
> >>>>action is taken in vfio_listener_region_del.
> >>>>
> >>>>When creating a new window, this uses euristic to decide on the TCE table
> >>>>levels number.
> >>>>
> >>>>This should cause no guest visible change in behavior.
> >>>>
> >>>>Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> >>>>---
> >>>>Changes:
> >>>>v14:
> >>>>* new to the series
> >>>>
> >>>>---
> >>>>TODO:
> >>>>* export levels to PHB
> >>>>---
> >>>>  hw/vfio/common.c | 108 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
> >>>>  trace-events     |   2 ++
> >>>>  2 files changed, 105 insertions(+), 5 deletions(-)
> >>>>
> >>>>diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> >>>>index 4e873b7..421d6eb 100644
> >>>>--- a/hw/vfio/common.c
> >>>>+++ b/hw/vfio/common.c
> >>>>@@ -279,6 +279,14 @@ static int vfio_host_iommu_add(VFIOContainer *container,
> >>>>      return 0;
> >>>>  }
> >>>>
> >>>>+static void vfio_host_iommu_del(VFIOContainer *container, hwaddr min_iova)
> >>>>+{
> >>>>+    VFIOHostIOMMU *hiommu = vfio_host_iommu_lookup(container, min_iova, 0x1000);
> >>>
> >>>The hard-coded 0x1000 looks dubious..
> >>
> >>Well, that's the minimal page size...
> >
> >Really?  Some BookE CPUs support 1KiB page size..
> 
> Hm. For IOMMU? Ok. s/0x1000/1/ should do then :)

Uh.. actually I don't think those CPUs generally had an IOMMU.  But if
it's been done for CPU MMU I wouldn't count on it not being done for
IOMMU.

1 is a safer choice.

> 
> 
> >
> >>>>+    g_assert(hiommu);
> >>>>+    QLIST_REMOVE(hiommu, hiommu_next);
> >>>>+}
> >>>>+
> >>>>  static bool vfio_listener_skipped_section(MemoryRegionSection *section)
> >>>>  {
> >>>>      return (!memory_region_is_ram(section->mr) &&
> >>>>@@ -392,6 +400,61 @@ static void vfio_listener_region_add(MemoryListener *listener,
> >>>>      }
> >>>>      end = int128_get64(llend);
> >>>>
> >>>>+    if (container->iommu_type == VFIO_SPAPR_TCE_v2_IOMMU) {
> >>>
> >>>I think this would be clearer split out into a helper function,
> >>>vfio_create_host_window() or something.
> >>
> >>
> >>It is rather vfio_spapr_create_host_window() and we were avoiding
> >>xxx_spapr_xxx so far. I'd cut-n-paste the SPAPR PCI AS listener to a
> >>separate file but this usually triggers more discussion and never ends well.
> >>
> >>
> >>
> >>>>+        unsigned entries, pages;
> >>>>+        struct vfio_iommu_spapr_tce_create create = { .argsz = sizeof(create) };
> >>>>+
> >>>>+        g_assert(section->mr->iommu_ops);
> >>>>+        g_assert(memory_region_is_iommu(section->mr));
> >>>
> >>>I don't think you need these asserts.  AFAICT the same logic should
> >>>work if a RAM MR was added directly to PCI address space - this would
> >>>create the new host window, then the existing code for adding a RAM MR
> >>>would map that block of RAM statically into the new window.
> >>
> >>In what configuration/machine can we do that on SPAPR?
> >
> >spapr guests won't ever do that.  But you can run an x86 guest on a
> >powernv host and this situation could come up.
> 
> 
> I am pretty sure VFIO won't work in this case anyway.

I'm not.  There's no fundamental reason VFIO shouldn't work with TCG.

> >In any case there's no point asserting if the code is correct anyway.
> 
> Assert here says (at least) "not tested" or "not expected to
> happen".

Hmmm..

> 
> 
> >
> >>>>+        trace_vfio_listener_region_add_iommu(iova, end - 1);
> >>>>+        /*
> >>>>+         * FIXME: For VFIO iommu types which have KVM acceleration to
> >>>>+         * avoid bouncing all map/unmaps through qemu this way, this
> >>>>+         * would be the right place to wire that up (tell the KVM
> >>>>+         * device emulation the VFIO iommu handles to use).
> >>>>+         */
> >>>>+        create.window_size = memory_region_size(section->mr);
> >>>>+        create.page_shift =
> >>>>+                ctz64(section->mr->iommu_ops->get_page_sizes(section->mr));
> >>>
> >>>Ah.. except that I guess you'd need to fall back to host page size
> >>>here to handle a RAM MR.
> >>
> >>Can you give an example of such RAM MR being added to PCI AS on
> >>SPAPR?
> >
> >On spapr, no.  But you can run other machine types as guests (at least
> >with TCG) on a host with the spapr IOMMU.
> >
> >>>>+        /*
> >>>>+         * SPAPR host supports multilevel TCE tables, there is some
> >>>>+         * euristic to decide how many levels we want for our table:
> >>>>+         * 0..64 = 1; 65..4096 = 2; 4097..262144 = 3; 262145.. = 4
> >>>>+         */
> >>>>+        entries = create.window_size >> create.page_shift;
> >>>>+        pages = (entries * sizeof(uint64_t)) / getpagesize();
> >>>>+        create.levels = ctz64(pow2ceil(pages) - 1) / 6 + 1;
> >>>>+
> >>>>+        ret = ioctl(container->fd, VFIO_IOMMU_SPAPR_TCE_CREATE, &create);
> >>>>+        if (ret) {
> >>>>+            error_report("Failed to create a window, ret = %d (%m)", ret);
> >>>>+            goto fail;
> >>>>+        }
> >>>>+
> >>>>+        if (create.start_addr != section->offset_within_address_space ||
> >>>>+            vfio_host_iommu_lookup(container, create.start_addr,
> >>>>+                                   create.start_addr + create.window_size - 1)) {
> >>>
> >>>Under what circumstances can this trigger?  Is the kernel ioctl
> >>>allowed to return a different window start address than the one
> >>>requested?
> >>
> >>You already asked this some time ago :) The userspace cannot request
> >>address, the host kernel returns one.
> >
> >Ok.  For generality it would be nice if you could succeed here as long
> >as the new host window covers the requested guest window, even if it
> >doesn't match exactly.  And for that matter to not request the new
> >window if the host already has a window covering the guest region.
> 
> 
> That would be dead code - when would it possibly work? I mean I could
> instrument an artificial test but the actual user which might appear later
> will likely be soooo different so this won't help anyway.

Hmm, I suppose.  It actually shouldn't be that hard to trigger a case
like this, if you just bumped the bridge's dma64 base address property
up a little bit - above the host kernel's base address, but small
enough that you can still easily fit the guest memory in.

> >>>The second check looks very strange - if it returns true doesn't that
> >>>mean you *do* have host window which can accomodate this guest region,
> >>>which is what you want?
> >>
> >>This should not happen, this is what this check is for. Can make it assert()
> >>or something like this.
> >
> >Oh.. I see.  Because you've done the ioctl, but not recorded the new
> >host window in the list yet.
> >
> >No, I think the correct approach is to look for an existing host
> >window containing the requested guest window *before* you try to
> >create a new host window.  If one is already there, you can just carry
> >on.
> 
> Right, I'll change this.
> 
> 
> >
> >>>>+            struct vfio_iommu_spapr_tce_remove remove = {
> >>>>+                .argsz = sizeof(remove),
> >>>>+                .start_addr = create.start_addr
> >>>>+            };
> >>>>+            error_report("Host doesn't support DMA window at %"HWADDR_PRIx", must be %"PRIx64,
> >>>>+                         section->offset_within_address_space,
> >>>>+                         create.start_addr);
> >>>>+            ioctl(container->fd, VFIO_IOMMU_SPAPR_TCE_REMOVE, &remove);
> >>>>+            ret = -EINVAL;
> >>>>+            goto fail;
> >>>>+        }
> >>>>+        trace_vfio_spapr_create_window(create.page_shift,
> >>>>+                                       create.window_size,
> >>>>+                                       create.start_addr);
> >>>>+
> >>>>+        vfio_host_iommu_add(container, create.start_addr,
> >>>>+                            create.start_addr + create.window_size - 1,
> >>>>+                            1ULL << create.page_shift);
> >>>>+    }
> >>>>+
> >>>>      if (!vfio_host_iommu_lookup(container, iova, end - 1)) {
> >>>>          error_report("vfio: IOMMU container %p can't map guest IOVA region"
> >>>>                       " 0x%"HWADDR_PRIx"..0x%"HWADDR_PRIx,
> >>>>@@ -525,6 +588,22 @@ static void vfio_listener_region_del(MemoryListener *listener,
> >>>>                       container, iova, end - iova, ret);
> >>>>      }
> >>>>
> >>>>+    if (container->iommu_type == VFIO_SPAPR_TCE_v2_IOMMU) {
> >>>>+        struct vfio_iommu_spapr_tce_remove remove = {
> >>>>+            .argsz = sizeof(remove),
> >>>>+            .start_addr = section->offset_within_address_space,
> >>>>+        };
> >>>>+        ret = ioctl(container->fd, VFIO_IOMMU_SPAPR_TCE_REMOVE, &remove);
> >>>>+        if (ret) {
> >>>>+            error_report("Failed to remove window at %"PRIx64,
> >>>>+                         remove.start_addr);
> >>>>+        }
> >>>>+
> >>>>+        vfio_host_iommu_del(container, section->offset_within_address_space);
> >>>>+
> >>>>+        trace_vfio_spapr_remove_window(remove.start_addr);
> >>>>+    }
> >>>>+
> >>>>      if (iommu && iommu->iommu_ops && iommu->iommu_ops->vfio_stop) {
> >>>>          iommu->iommu_ops->vfio_stop(section->mr);
> >>>>      }
> >>>>@@ -928,11 +1007,30 @@ static int vfio_connect_container(VFIOGroup *group, AddressSpace *as)
> >>>>              goto listener_release_exit;
> >>>>          }
> >>>>
> >>>>-        /* The default table uses 4K pages */
> >>>>-        vfio_host_iommu_add(container, info.dma32_window_start,
> >>>>-                            info.dma32_window_start +
> >>>>-                            info.dma32_window_size - 1,
> >>>>-                            0x1000);
> >>>>+        if (v2) {
> >>>>+            /*
> >>>>+             * There is a default window in just created container.
> >>>>+             * To make region_add/del simpler, we better remove this
> >>>>+             * window now and let those iommu_listener callbacks
> >>>>+             * create/remove them when needed.
> >>>>+             */
> >>>>+            struct vfio_iommu_spapr_tce_remove remove = {
> >>>>+                .argsz = sizeof(remove),
> >>>>+                .start_addr = info.dma32_window_start,
> >>>>+            };
> >>>>+            ret = ioctl(fd, VFIO_IOMMU_SPAPR_TCE_REMOVE, &remove);
> >>>>+            if (ret) {
> >>>>+                error_report("vfio: VFIO_IOMMU_SPAPR_TCE_REMOVE failed: %m");
> >>>>+                ret = -errno;
> >>>>+                goto free_container_exit;
> >>>>+            }
> >>>>+        } else {
> >>>>+            /* The default table uses 4K pages */
> >>>>+            vfio_host_iommu_add(container, info.dma32_window_start,
> >>>>+                                info.dma32_window_start +
> >>>>+                                info.dma32_window_size - 1,
> >>>>+                                0x1000);
> >>>>+        }
> >>>>      } else {
> >>>>          error_report("vfio: No available IOMMU models");
> >>>>          ret = -EINVAL;
> >>>>diff --git a/trace-events b/trace-events
> >>>>index cc619e1..f2b75a3 100644
> >>>>--- a/trace-events
> >>>>+++ b/trace-events
> >>>>@@ -1736,6 +1736,8 @@ vfio_region_finalize(const char *name, int index) "Device %s, region %d"
> >>>>  vfio_region_mmaps_set_enabled(const char *name, bool enabled) "Region %s mmaps enabled: %d"
> >>>>  vfio_ram_register(uint64_t va, uint64_t size, int ret) "va=%"PRIx64" size=%"PRIx64" ret=%d"
> >>>>  vfio_ram_unregister(uint64_t va, uint64_t size, int ret) "va=%"PRIx64" size=%"PRIx64" ret=%d"
> >>>>+vfio_spapr_create_window(int ps, uint64_t ws, uint64_t off) "pageshift=0x%x winsize=0x%"PRIx64" offset=0x%"PRIx64
> >>>>+vfio_spapr_remove_window(uint64_t off) "offset=%"PRIx64
> >>>>
> >>>>  # hw/vfio/platform.c
> >>>>  vfio_platform_base_device_init(char *name, int groupid) "%s belongs to group #%d"
> >>>
> >>
> >>
> >
> 
> 

-- 
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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