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

[David Gibson]

On Thu, Mar 24, 2016 at 08:10:44PM +1100, Alexey Kardashevskiy wrote:
> On 03/24/2016 11:03 AM, Alexey Kardashevskiy wrote:
> >On 03/23/2016 05:03 PM, David Gibson wrote:
> >>On Wed, Mar 23, 2016 at 02:06:36PM +1100, Alexey Kardashevskiy wrote:
> >>>On 03/23/2016 01:53 PM, David Gibson wrote:
> >>>>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 <address@hidden>
> >>>>>>>>>---
> >>>>>>>>>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.
> >>>
> >>>This is not about TCG (pseries TCG guest works with VFIO on powernv host),
> >>>this is about things like VFIO_IOMMU_GET_INFO vs.
> >>>VFIO_IOMMU_SPAPR_TCE_GET_INFO ioctls but yes, fundamentally, it can work.
> >>>
> >>>Should I add such support in this patchset?
> >>
> >>Unless adding the generality is really complex, and so far I haven't
> >>seen a reason for it to be.
> >
> >Seriously? :(
> 
> 
> So, I tried.
> 
> With q35 machine (pc-i440fx-2.6 have even worse memory tree), there are
> several RAM blocks - 0..0xc0000, then pc.rom, then RAM again till 2GB, then
> a gap (PCI MMIO?), then PC BIOS at 0xfffc0000 (which is RAM), then after 4GB
> the rest of the RAM:
> 
> memory-region: system
>   0000000000000000-ffffffffffffffff (prio 0, RW): system
>     0000000000000000-000000007fffffff (prio 0, RW): alias ram-below-4g
> @pc.ram 0000000000000000-000000007fffffff
>     0000000000000000-ffffffffffffffff (prio -1, RW): pci
>       00000000000c0000-00000000000dffff (prio 1, RW): pc.rom
>       00000000000e0000-00000000000fffff (prio 1, R-): alias isa-bios
> @pc.bios 0000000000020000-000000000003ffff
>       00000000febe0000-00000000febeffff (prio 1, RW): 0003:09:00.0 BAR 0
>         00000000febe0000-00000000febeffff (prio 0, RW): 0003:09:00.0 BAR 0
> mmaps[0]
>       00000000febf0000-00000000febf1fff (prio 1, RW): 0003:09:00.0 BAR 2
>         00000000febf0000-00000000febf007f (prio 0, RW): msix-table
>         00000000febf1000-00000000febf1007 (prio 0, RW): msix-pba [disabled]
>       00000000febf2000-00000000febf2fff (prio 1, RW): ahci
>       00000000fffc0000-00000000ffffffff (prio 0, R-): pc.bios
> [...]
>     0000000100000000-000000027fffffff (prio 0, RW): alias ram-above-4g
> @pc.ram 0000000080000000-00000001ffffffff
> 
> 
> Ok, let's say we filter out "pc.bios", "pc.rom", BARs (aka "skip dump"
> regions) and we end up having RAM below 2GB and above 4GB, 2 windows.
> Problem is a window needs to be aligned to power of two.

Window size?  That should be ok - you can just round up the requested
size to a power of two.  We don't have to populate the whole host window.

> Ok, I change my test from -m8G to -m10G to have 2 aligned regions - 2GB and
> 8GB), next problem - the second window needs to start from 1<<<59, not 4G or
> any other random offset.

Yeah, that's harder.  With the IODA is it always that the 32-bit
window is at 0 and the 64-bit window is at 1<<59, or can you have a
64-bit window at 0?

If it's the second, then this is theoretically possible, but the host
kernel - on seeing the second window request, would need to see that
it can instead of adding a new host window, instead extend the first
host window so that it covers both the guest windows.

That does sound reasonably tricky and I don't think we should try to
implement it any time soon.  BUT - we should design our *interfaces*
so that it's reasonable to add that in future.

> Ok, I change my test to start with -m1G to have a single window.
> Now it fails because here is what happens:
> region_add: pc.ram: 0 40000000
> region_del: pc.ram: 0 40000000
> region_add: pc.ram: 0 c0000
> The second "add" is not power of two -> fail. And I cannot avoid this -
> "pc.rom" is still there, it is a separate region so RAM gets split into
> smaller chunks. I do not know to to fix this properly.
> 
> 
> So, in order to make it (x86/tcg on powernv host) work anyhow, I had to
> create a single huge window (as it is a single window - it starts from @0)
> unconditionally in vfio_connect_container(), not in
> vfio_listener_region_add(); and I added filtering (skip "pc.bios", "pc.rom",
> BARs - these things start above 1GB) and then I could boot a x86_64 guest
> and even pass Mellanox ConnextX3, it would bring 2 interfaces up and
> dhclient assigned IPs to them (which is quite amusing that it even works).
> 
> 
> So, I think I will replace assert() with:
> 
> unsigned pagesize = qemu_real_host_page_size;
> if (section->mr->iommu_ops) {
>     pagesize = section->mr->iommu_ops->get_page_sizes(section->mr);
> }
> 
> but there is no practical use for this anyway.

So, I think what you need here is to compute the effective IOMMU page
size (see other email for details).  That will be getrampagesize() for
RAM regions, and the mininum of that and the guest IOMMU page size for
IOMMU regions.

-- 
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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