From: David Gibson <david@gibson.dropbear.id.au>
To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: Gavin Shan <gwshan@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org,
Alex Williamson <alex.williamson@redhat.com>,
Paul Mackerras <paulus@samba.org>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH kernel v9 27/32] powerpc/iommu/ioda2: Add get_table_size() to calculate the size of future table
Date: Tue, 5 May 2015 21:58:13 +1000 [thread overview]
Message-ID: <20150505115813.GL14090@voom.redhat.com> (raw)
In-Reply-To: <554322D4.7070508@ozlabs.ru>
[-- Attachment #1: Type: text/plain, Size: 7470 bytes --]
On Fri, May 01, 2015 at 04:53:08PM +1000, Alexey Kardashevskiy wrote:
> On 05/01/2015 03:12 PM, David Gibson wrote:
> >On Fri, May 01, 2015 at 02:10:58PM +1000, Alexey Kardashevskiy wrote:
> >>On 04/29/2015 04:40 PM, David Gibson wrote:
> >>>On Sat, Apr 25, 2015 at 10:14:51PM +1000, Alexey Kardashevskiy wrote:
> >>>>This adds a way for the IOMMU user to know how much a new table will
> >>>>use so it can be accounted in the locked_vm limit before allocation
> >>>>happens.
> >>>>
> >>>>This stores the allocated table size in pnv_pci_create_table()
> >>>>so the locked_vm counter can be updated correctly when a table is
> >>>>being disposed.
> >>>>
> >>>>This defines an iommu_table_group_ops callback to let VFIO know
> >>>>how much memory will be locked if a table is created.
> >>>>
> >>>>Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> >>>>---
> >>>>Changes:
> >>>>v9:
> >>>>* reimplemented the whole patch
> >>>>---
> >>>> arch/powerpc/include/asm/iommu.h | 5 +++++
> >>>> arch/powerpc/platforms/powernv/pci-ioda.c | 14 ++++++++++++
> >>>> arch/powerpc/platforms/powernv/pci.c | 36 +++++++++++++++++++++++++++++++
> >>>> arch/powerpc/platforms/powernv/pci.h | 2 ++
> >>>> 4 files changed, 57 insertions(+)
> >>>>
> >>>>diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
> >>>>index 1472de3..9844c106 100644
> >>>>--- a/arch/powerpc/include/asm/iommu.h
> >>>>+++ b/arch/powerpc/include/asm/iommu.h
> >>>>@@ -99,6 +99,7 @@ struct iommu_table {
> >>>> unsigned long it_size; /* Size of iommu table in entries */
> >>>> unsigned long it_indirect_levels;
> >>>> unsigned long it_level_size;
> >>>>+ unsigned long it_allocated_size;
> >>>> unsigned long it_offset; /* Offset into global table */
> >>>> unsigned long it_base; /* mapped address of tce table */
> >>>> unsigned long it_index; /* which iommu table this is */
> >>>>@@ -155,6 +156,10 @@ extern struct iommu_table *iommu_init_table(struct iommu_table * tbl,
> >>>> struct iommu_table_group;
> >>>>
> >>>> struct iommu_table_group_ops {
> >>>>+ unsigned long (*get_table_size)(
> >>>>+ __u32 page_shift,
> >>>>+ __u64 window_size,
> >>>>+ __u32 levels);
> >>>> long (*create_table)(struct iommu_table_group *table_group,
> >>>> int num,
> >>>> __u32 page_shift,
> >>>>diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> >>>>index e0be556..7f548b4 100644
> >>>>--- a/arch/powerpc/platforms/powernv/pci-ioda.c
> >>>>+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> >>>>@@ -2062,6 +2062,18 @@ static void pnv_pci_ioda2_setup_bypass_pe(struct pnv_phb *phb,
> >>>> }
> >>>>
> >>>> #ifdef CONFIG_IOMMU_API
> >>>>+static unsigned long pnv_pci_ioda2_get_table_size(__u32 page_shift,
> >>>>+ __u64 window_size, __u32 levels)
> >>>>+{
> >>>>+ unsigned long ret = pnv_get_table_size(page_shift, window_size, levels);
> >>>>+
> >>>>+ if (!ret)
> >>>>+ return ret;
> >>>>+
> >>>>+ /* Add size of it_userspace */
> >>>>+ return ret + (window_size >> page_shift) * sizeof(unsigned long);
> >>>
> >>>This doesn't make much sense. The userspace view can't possibly be a
> >>>property of the specific low-level IOMMU model.
> >>
> >>
> >>This it_userspace thing is all about memory preregistration.
> >>
> >>I need some way to track how many actual mappings the
> >>mm_iommu_table_group_mem_t has in order to decide whether to allow
> >>unregistering or not.
> >>
> >>When I clear TCE, I can read the old value which is host physical address
> >>which I cannot use to find the preregistered region and adjust the mappings
> >>counter; I can only use userspace addresses for this (not even guest
> >>physical addresses as it is VFIO and probably no KVM).
> >>
> >>So I have to keep userspace addresses somewhere, one per IOMMU page, and the
> >>iommu_table seems a natural place for this.
> >
> >Well.. sort of. But as noted elsewhere this pulls VFIO specific
> >constraints into a platform code structure. And whether you get this
> >table depends on the platform IOMMU type rather than on what VFIO
> >wants to do with it, which doesn't make sense.
> >
> >What might make more sense is an opaque pointer io iommu_table for use
> >by the table "owner" (in the take_ownership sense). The pointer would
> >be stored in iommu_table, but VFIO is responsible for populating and
> >managing its contents.
> >
> >Or you could just put the userspace mappings in the container.
> >Although you might want a different data structure in that case.
>
> Nope. I need this table in in-kernel acceleration to update the mappings
> counter per mm_iommu_table_group_mem_t. In KVM's real mode handlers, I only
> have IOMMU tables, not containers or groups. QEMU creates a guest view of
> the table (KVM_CREATE_SPAPR_TCE) specifying a LIOBN, and then attaches TCE
> tables to it via set of ioctls (one per IOMMU group) to VFIO KVM device.
>
> So if I call it it_opaque (instead of it_userspace), I will still need a
> common place (visible to VFIO and PowerKVM) for this to put:
> #define IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry)
I think it should be in a VFIO header. If I'm understanding right
this part of the PowerKVM code is explicitly VFIO aware - that's kind
of the point.
> So far this place was arch/powerpc/include/asm/iommu.h and the iommu_table
> struct.
>
>
> >The other thing to bear in mind is that registered regions are likely
> >to be large contiguous blocks in user addresses, though obviously not
> >contiguous in physical addr. So you might be able to compaticfy this
> >information by storing it as a list of variable length blocks in
> >userspace address space, rather than a per-page address..
>
> It is 8 bytes per system page - 8/65536 = 0.00012 (or 26MB for 200GB guest)
> - very little overhead.
>
>
> >But.. isn't there a bigger problem here. As Paulus was pointing out,
> >there's nothing guaranteeing the page tables continue to contain the
> >same page as was there at gup() time.
>
> This can happen if the userspace remaps memory which it registered/mapped
> for DMA via VFIO, no? If so, then the userspace just should not do this, it
> is DMA, it cannot be moved like this. What am I missing here?
>
>
> >What's going to happen if you REGISTER a memory region, then mremap()
> >over it?
>
> The registered pages will remain pinned and PUT_TCE will use that region for
> translation (and this will fail as the userspace addresses changed).
>
> I do not see how it is different from the situation when the userspace
> mapped a page and mremap()ed it while it is DMA-mapped.
True, it's basically the same. Hrm, so what guarantees a dma_map,
mremap() dma_unmap will unreference the correct pages.
> >Then attempt to PUT_TCE a page in the region? Or what if you
> >mremap() it to someplace else then try to PUT_TCE a page there?
>
> This will fail - a new userspace address has to be preregistered.
>
> >Or REGISTER it again in its new location?
>
> It will be pinned twice + some memory overhead to store the same host
> physical address(es) twice.
>
>
>
--
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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next prev parent reply other threads:[~2015-05-05 13:09 UTC|newest]
Thread overview: 110+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-25 12:14 [PATCH kernel v9 00/32] powerpc/iommu/vfio: Enable Dynamic DMA windows Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 01/32] powerpc/iommu: Split iommu_free_table into 2 helpers Alexey Kardashevskiy
2015-04-29 2:03 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 02/32] Revert "powerpc/powernv: Allocate struct pnv_ioda_pe iommu_table dynamically" Alexey Kardashevskiy
2015-04-27 21:05 ` Alex Williamson
2015-04-29 2:05 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 03/32] vfio: powerpc/spapr: Move page pinning from arch code to VFIO IOMMU driver Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 04/32] vfio: powerpc/spapr: Check that IOMMU page is fully contained by system page Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 05/32] vfio: powerpc/spapr: Use it_page_size Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 06/32] vfio: powerpc/spapr: Move locked_vm accounting to helpers Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 07/32] vfio: powerpc/spapr: Disable DMA mappings on disabled container Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 08/32] vfio: powerpc/spapr: Moving pinning/unpinning to helpers Alexey Kardashevskiy
2015-04-29 2:14 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 09/32] vfio: powerpc/spapr: Rework groups attaching Alexey Kardashevskiy
2015-04-29 2:16 ` David Gibson
2015-04-30 2:29 ` Alexey Kardashevskiy
2015-04-30 4:05 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 10/32] powerpc/powernv: Do not set "read" flag if direction==DMA_NONE Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 11/32] powerpc/iommu: Move tce_xxx callbacks from ppc_md to iommu_table Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 12/32] powerpc/spapr: vfio: Switch from iommu_table to new iommu_table_group Alexey Kardashevskiy
2015-04-29 2:49 ` David Gibson
2015-04-30 2:30 ` Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 13/32] vfio: powerpc/spapr/iommu/powernv/ioda2: Rework IOMMU ownership control Alexey Kardashevskiy
2015-04-29 3:02 ` David Gibson
2015-04-29 9:19 ` Alexey Kardashevskiy
2015-04-30 4:08 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 14/32] powerpc/iommu: Fix IOMMU ownership control functions Alexey Kardashevskiy
2015-04-29 3:08 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 15/32] powerpc/powernv/ioda/ioda2: Rework TCE invalidation in tce_build()/tce_free() Alexey Kardashevskiy
2015-04-29 3:18 ` David Gibson
2015-04-30 2:58 ` Alexey Kardashevskiy
2015-04-30 4:16 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 16/32] powerpc/powernv/ioda: Move TCE kill register address to PE Alexey Kardashevskiy
2015-04-27 21:05 ` Alex Williamson
2015-04-29 3:25 ` David Gibson
2015-04-29 9:00 ` Alexey Kardashevskiy
2015-04-30 4:18 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 17/32] powerpc/powernv: Implement accessor to TCE entry Alexey Kardashevskiy
2015-04-29 4:04 ` David Gibson
2015-04-29 9:02 ` Alexey Kardashevskiy
2015-04-30 0:13 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 18/32] powerpc/iommu/powernv: Release replaced TCE Alexey Kardashevskiy
2015-04-29 4:18 ` David Gibson
2015-04-29 9:51 ` Alexey Kardashevskiy
2015-04-30 4:21 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 19/32] powerpc/powernv/ioda2: Rework iommu_table creation Alexey Kardashevskiy
2015-04-29 4:27 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 20/32] powerpc/powernv/ioda2: Introduce pnv_pci_create_table/pnv_pci_free_table Alexey Kardashevskiy
2015-04-29 4:39 ` David Gibson
2015-04-29 9:12 ` Alexey Kardashevskiy
2015-04-30 4:24 ` David Gibson
2015-05-01 10:13 ` Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 21/32] powerpc/powernv/ioda2: Introduce pnv_pci_ioda2_set_window Alexey Kardashevskiy
2015-04-29 4:45 ` David Gibson
2015-04-29 9:26 ` Alexey Kardashevskiy
2015-04-30 4:32 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 22/32] powerpc/powernv: Implement multilevel TCE tables Alexey Kardashevskiy
2015-04-29 5:04 ` David Gibson
2015-05-01 9:48 ` Alexey Kardashevskiy
2015-05-05 12:05 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 23/32] powerpc/powernv/ioda: Define and implement DMA table/window management callbacks Alexey Kardashevskiy
2015-04-29 5:30 ` David Gibson
2015-04-29 9:44 ` Alexey Kardashevskiy
2015-04-30 4:37 ` David Gibson
2015-04-30 9:56 ` Alexey Kardashevskiy
2015-05-01 3:36 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 24/32] powerpc/powernv/ioda2: Use new helpers to do proper cleanup on PE release Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 25/32] vfio: powerpc/spapr: powerpc/powernv/ioda2: Rework ownership Alexey Kardashevskiy
2015-04-29 5:39 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 26/32] powerpc/iommu: Add userspace view of TCE table Alexey Kardashevskiy
2015-04-29 6:31 ` David Gibson
2015-05-01 4:01 ` Alexey Kardashevskiy
2015-05-01 4:23 ` David Gibson
2015-05-01 7:12 ` Alexey Kardashevskiy
2015-05-05 12:02 ` David Gibson
2015-05-11 2:11 ` Alexey Kardashevskiy
2015-05-11 4:52 ` Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 27/32] powerpc/iommu/ioda2: Add get_table_size() to calculate the size of future table Alexey Kardashevskiy
2015-04-29 6:40 ` David Gibson
2015-05-01 4:10 ` Alexey Kardashevskiy
2015-05-01 5:12 ` David Gibson
2015-05-01 6:53 ` Alexey Kardashevskiy
2015-05-05 11:58 ` David Gibson [this message]
2015-05-11 2:24 ` Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 28/32] powerpc/mmu: Add userspace-to-physical addresses translation cache Alexey Kardashevskiy
2015-04-29 7:01 ` David Gibson
2015-05-01 11:26 ` Alexey Kardashevskiy
2015-05-05 12:12 ` David Gibson
2015-04-30 6:34 ` David Gibson
2015-04-30 8:25 ` Paul Mackerras
2015-05-01 3:39 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 29/32] vfio: powerpc/spapr: Register memory and define IOMMU v2 Alexey Kardashevskiy
2015-04-30 6:55 ` David Gibson
2015-05-01 4:35 ` Alexey Kardashevskiy
2015-05-01 5:23 ` David Gibson
2015-05-01 6:27 ` Alexey Kardashevskiy
2015-05-05 11:53 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 30/32] vfio: powerpc/spapr: Use 32bit DMA window properties from table_group Alexey Kardashevskiy
2015-04-27 22:18 ` Alex Williamson
2015-04-30 6:58 ` David Gibson
2015-04-25 12:14 ` [PATCH kernel v9 31/32] vfio: powerpc/spapr: Support multiple groups in one container if possible Alexey Kardashevskiy
2015-04-30 7:22 ` David Gibson
2015-04-30 9:33 ` Alexey Kardashevskiy
2015-05-01 0:46 ` Benjamin Herrenschmidt
2015-05-01 4:44 ` David Gibson
2015-05-01 4:33 ` David Gibson
2015-05-01 6:05 ` Alexey Kardashevskiy
2015-05-05 11:50 ` David Gibson
2015-05-11 2:26 ` Alexey Kardashevskiy
2015-04-25 12:14 ` [PATCH kernel v9 32/32] vfio: powerpc/spapr: Support Dynamic DMA windows Alexey Kardashevskiy
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