[PATCH 6/8] drm/xe: Helper to populate a userptr or hmmptr
Zeng, Oak
oak.zeng at intel.com
Tue Mar 19 17:59:04 UTC 2024
Hi Matt,
> -----Original Message-----
> From: Brost, Matthew <matthew.brost at intel.com>
> Sent: Tuesday, March 19, 2024 12:49 PM
> To: Hellstrom, Thomas <thomas.hellstrom at intel.com>
> Cc: intel-xe at lists.freedesktop.org; Zeng, Oak <oak.zeng at intel.com>; Welty,
> Brian <brian.welty at intel.com>; Ghimiray, Himal Prasad
> <himal.prasad.ghimiray at intel.com>
> Subject: Re: [PATCH 6/8] drm/xe: Helper to populate a userptr or hmmptr
>
> On Tue, Mar 19, 2024 at 04:33:39AM -0600, Hellstrom, Thomas wrote:
> > On Mon, 2024-03-18 at 22:55 -0400, Oak Zeng wrote:
> > > Add a helper function xe_userptr_populate_range to populate
> > > a a userptr or hmmptr range. This functions calls hmm_range_fault
> > > to read CPU page tables and populate all pfns/pages of this
> > > virtual address range.
> > >
> > > If the populated page is system memory page, dma-mapping is performed
> > > to get a dma-address which can be used later for GPU to access pages.
> > >
> > > If the populated page is device private page, we calculate the dpa (
> > > device physical address) of the page.
> > >
> > > The dma-address or dpa is then saved in userptr's sg table. This is
> > > prepare work to replace the get_user_pages_fast code in userptr code
> > > path. The helper function will also be used to populate hmmptr later.
> > >
> > > v1: Address review comments:
> > > separate a npage_in_range function (Matt)
> > > reparameterize function xe_userptr_populate_range function (Matt)
> > > move mmu_interval_read_begin() call into while loop (Thomas)
> > > s/mark_range_accessed/xe_mark_range_accessed (Thomas)
> > > use set_page_dirty_lock (vs set_page_dirty) (Thomas)
> > > move a few checking in xe_vma_userptr_pin_pages to hmm.c (Matt)
> > >
> > > Signed-off-by: Oak Zeng <oak.zeng at intel.com>
> > > Co-developed-by: Niranjana Vishwanathapura
> > > <niranjana.vishwanathapura at intel.com>
> > > Signed-off-by: Niranjana Vishwanathapura
> > > <niranjana.vishwanathapura at intel.com>
> > > Cc: Matthew Brost <matthew.brost at intel.com>
> > > Cc: Thomas Hellström <thomas.hellstrom at intel.com>
> > > Cc: Brian Welty <brian.welty at intel.com>
> > > ---
> > > drivers/gpu/drm/xe/Makefile | 1 +
> > > drivers/gpu/drm/xe/xe_hmm.c | 231
> > > ++++++++++++++++++++++++++++++++++++
> > > drivers/gpu/drm/xe/xe_hmm.h | 10 ++
> > > 3 files changed, 242 insertions(+)
> > > create mode 100644 drivers/gpu/drm/xe/xe_hmm.c
> > > create mode 100644 drivers/gpu/drm/xe/xe_hmm.h
> > >
> > > diff --git a/drivers/gpu/drm/xe/Makefile
> > > b/drivers/gpu/drm/xe/Makefile
> > > index e2ec6d1375c0..52300de1e86f 100644
> > > --- a/drivers/gpu/drm/xe/Makefile
> > > +++ b/drivers/gpu/drm/xe/Makefile
> > > @@ -101,6 +101,7 @@ xe-y += xe_bb.o \
> > > xe_guc_pc.o \
> > > xe_guc_submit.o \
> > > xe_heci_gsc.o \
> > > + xe_hmm.o \
> > > xe_hw_engine.o \
> > > xe_hw_engine_class_sysfs.o \
> > > xe_hw_fence.o \
> > > diff --git a/drivers/gpu/drm/xe/xe_hmm.c
> > > b/drivers/gpu/drm/xe/xe_hmm.c
> > > new file mode 100644
> > > index 000000000000..305e3f2e659b
> > > --- /dev/null
> > > +++ b/drivers/gpu/drm/xe/xe_hmm.c
> > > @@ -0,0 +1,231 @@
> > > +// SPDX-License-Identifier: MIT
> > > +/*
> > > + * Copyright © 2024 Intel Corporation
> > > + */
> > > +
> > > +#include <linux/mmu_notifier.h>
> > > +#include <linux/dma-mapping.h>
> > > +#include <linux/memremap.h>
> > > +#include <linux/swap.h>
> > > +#include <linux/hmm.h>
> > > +#include <linux/mm.h>
> > > +#include "xe_hmm.h"
> > > +#include "xe_svm.h"
> > > +#include "xe_vm.h"
> > > +
> > > +static inline u64 npages_in_range(unsigned long start, unsigned long
> > > end)
> > > +{
> > > + return ((end - 1) >> PAGE_SHIFT) - (start >> PAGE_SHIFT) +
> > > 1;
> > > +}
> > > +
> > > +/**
> > > + * xe_mark_range_accessed() - mark a range is accessed, so core mm
> > > + * have such information for memory eviction or write back to
> > > + * hard disk
> > > + *
> > > + * @range: the range to mark
> > > + * @write: if write to this range, we mark pages in this range
> > > + * as dirty
> > > + */
> > > +static void xe_mark_range_accessed(struct hmm_range *range, bool
> > > write)
> > > +{
> > > + struct page *page;
> > > + u64 i, npages;
> > > +
> > > + npages = npages_in_range(range->start, range->end);
> > > + for (i = 0; i < npages; i++) {
> > > + page = hmm_pfn_to_page(range->hmm_pfns[i]);
> > > + if (write)
> > > + set_page_dirty_lock(page);
> > > +
> > > + mark_page_accessed(page);
> > > + }
> > > +}
> > > +
> > > +/**
> > > + * build_sg() - build a scatter gather table for all the physical
> > > pages/pfn
> > > + * in a hmm_range. dma-address is save in sg table and will be used
> > > to program
> > > + * GPU page table later.
> > > + *
> > > + * @xe: the xe device who will access the dma-address in sg table
> > > + * @range: the hmm range that we build the sg table from. range-
> > > >hmm_pfns[]
> > > + * has the pfn numbers of pages that back up this hmm address range.
> > > + * @st: pointer to the sg table.
> > > + * @write: whether we write to this range. This decides dma map
> > > direction
> > > + * for system pages. If write we map it bi-diretional; otherwise
> > > + * DMA_TO_DEVICE
> > > + *
> > > + * All the contiguous pfns will be collapsed into one entry in
> > > + * the scatter gather table. This is for the convenience of
> > > + * later on operations to bind address range to GPU page table.
> > > + *
> > > + * The dma_address in the sg table will later be used by GPU to
> > > + * access memory. So if the memory is system memory, we need to
> > > + * do a dma-mapping so it can be accessed by GPU/DMA. If the memory
> > > + * is GPU local memory (of the GPU who is going to access memory),
> > > + * we need gpu dpa (device physical address), and there is no need
> > > + * of dma-mapping.
> > > + *
> > > + * FIXME: dma-mapping for peer gpu device to access remote gpu's
> > > + * memory. Add this when you support p2p
> > > + *
> > > + * This function allocates the storage of the sg table. It is
> > > + * caller's responsibility to free it calling sg_free_table.
> > > + *
> > > + * Returns 0 if successful; -ENOMEM if fails to allocate memory
> > > + */
> > > +static int build_sg(struct xe_device *xe, struct hmm_range *range,
> > > + struct sg_table *st, bool write)
> > > +{
> > > + struct device *dev = xe->drm.dev;
> > > + struct scatterlist *sg;
> > > + u64 i, npages;
> > > +
> > > + sg = NULL;
> > > + st->nents = 0;
> > > + npages = npages_in_range(range->start, range->end);
> > > +
> > > + if (unlikely(sg_alloc_table(st, npages, GFP_KERNEL)))
> > > + return -ENOMEM;
> > > +
> > > + for (i = 0; i < npages; i++) {
> > > + struct page *page;
> > > + unsigned long addr;
> > > + struct xe_mem_region *mr;
> > > +
> > > + page = hmm_pfn_to_page(range->hmm_pfns[i]);
> > > + if (is_device_private_page(page)) {
> > > + mr = xe_page_to_mem_region(page);
> > > + addr = xe_mem_region_pfn_to_dpa(mr, range-
> > > >hmm_pfns[i]);
> > > + } else {
> > > + addr = dma_map_page(dev, page, 0, PAGE_SIZE,
> > > + write ? DMA_BIDIRECTIONAL :
> > > DMA_TO_DEVICE);
> > > + }
> >
> > The dma_map_page call here essentially stops the iommu from coalescing
> > the page-table into contigous iommu VAs, and stops us from using huge
> > page-table-entries for the PPGTT. IMO we should investigate whether we
> > could build a single scatter-gather using sg_alloc_table_from_pages()
> > or perhaps look at sg_alloc_append_table_from_pages(), and then use
> > dma_map_sg() on contiguous chunks of system pages within that sg-table.
> >
>
> Yes, this was my concern as well. I suggested we continue to use
> sg_alloc_table_from_pages_segment + dma_map_sgtable with only system
> support for now as device private page tables are still unused at the
> moment. That suggestion, among, other seems to have been ignored. I'm
> referring to my reply in [1], it would be nice to see those suggestions
> followed.
>
> Thomas is right about huge page-table-entries in the PPGTT. Add some
> printks if you need to see this in action (xe_pt_stage_bind_entry,
> xe_pt_hugepte_possible returning true).
>
> Make sure the IOMMU is enabled (intel_iommu=on on kernel cmdline) and run:
>
> xe_vm.large-userptr-binds-16777216 -> This will use 8x 2MB page tables on tip
> xe_vm.large-userptr-binds-2147483648 -> This will use 2x 1GB page tables on tip
>
> With your series it will likely use 4k pages for everything.
>
> Matt
>
> [1]
> https://patchwork.freedesktop.org/patch/582859/?series=131117&rev=1#comm
> ent_1064237
Damn, this comment was indeed overlooked...
Yes, both yours and Thomas' comments make a lot of sense to me. Let me follow up.
Oak
>
> > /Thomas
> >
> >
> > > +
> > > + if (sg && (addr == (sg_dma_address(sg) + sg-
> > > >length))) {
> > > + sg->length += PAGE_SIZE;
> > > + sg_dma_len(sg) += PAGE_SIZE;
> > > + continue;
> > > + }
> > > +
> > > + sg = sg ? sg_next(sg) : st->sgl;
> > > + sg_dma_address(sg) = addr;
> > > + sg_dma_len(sg) = PAGE_SIZE;
> > > + sg->length = PAGE_SIZE;
> > > + st->nents++;
> > > + }
> > > +
> > > + sg_mark_end(sg);
> > > + return 0;
> > > +}
> > > +
> > > +/**
> > > + * xe_userptr_populate_range() - Populate physical pages of a
> > > virtual
> > > + * address range
> > > + *
> > > + * @uvma: userptr vma which has information of the range to
> > > populate.
> > > + *
> > > + * This function populate the physical pages of a virtual
> > > + * address range. The populated physical pages is saved in
> > > + * userptr's sg table. It is similar to get_user_pages but call
> > > + * hmm_range_fault.
> > > + *
> > > + * This function also read mmu notifier sequence # (
> > > + * mmu_interval_read_begin), for the purpose of later
> > > + * comparison (through mmu_interval_read_retry).
> > > + *
> > > + * This must be called with mmap read or write lock held.
> > > + *
> > > + * This function allocates the storage of the userptr sg table.
> > > + * It is caller's responsibility to free it calling sg_free_table.
> > > + *
> > > + * returns: 0 for succuss; negative error no on failure
> > > + */
> > > +int xe_userptr_populate_range(struct xe_userptr_vma *uvma)
> > > +{
> > > + unsigned long timeout =
> > > + jiffies +
> > > msecs_to_jiffies(HMM_RANGE_DEFAULT_TIMEOUT);
> > > + unsigned long *pfns, flags = HMM_PFN_REQ_FAULT;
> > > + struct xe_userptr *userptr;
> > > + struct xe_vma *vma = &uvma->vma;
> > > + u64 start = xe_vma_userptr(vma);
> > > + u64 end = start + xe_vma_size(vma);
> > > + struct xe_vm *vm = xe_vma_vm(vma);
> > > + struct hmm_range hmm_range;
> > > + bool write = !xe_vma_read_only(vma);
> > > + bool in_kthread = !current->mm;
> > > + u64 npages;
> > > + int ret;
> > > +
> > > + userptr = &uvma->userptr;
> > > + mmap_assert_locked(userptr->notifier.mm);
> > > +
> > > + if (vma->gpuva.flags & XE_VMA_DESTROYED)
> > > + return 0;
> > > +
> > > + npages = npages_in_range(start, end);
> > > + pfns = kvmalloc_array(npages, sizeof(*pfns), GFP_KERNEL);
> > > + if (unlikely(!pfns))
> > > + return -ENOMEM;
> > > +
> > > + if (write)
> > > + flags |= HMM_PFN_REQ_WRITE;
> > > +
> > > + if (in_kthread) {
> > > + if (!mmget_not_zero(userptr->notifier.mm)) {
> > > + ret = -EFAULT;
> > > + goto free_pfns;
> > > + }
> > > + kthread_use_mm(userptr->notifier.mm);
> > > + }
> > > +
> > > + memset64((u64 *)pfns, (u64)flags, npages);
> > > + hmm_range.hmm_pfns = pfns;
> > > + hmm_range.notifier = &userptr->notifier;
> > > + hmm_range.start = start;
> > > + hmm_range.end = end;
> > > + hmm_range.pfn_flags_mask = HMM_PFN_REQ_FAULT |
> > > HMM_PFN_REQ_WRITE;
> > > + /**
> > > + * FIXME:
> > > + * Set the the dev_private_owner can prevent hmm_range_fault
> > > to fault
> > > + * in the device private pages owned by caller. See function
> > > + * hmm_vma_handle_pte. In multiple GPU case, this should be
> > > set to the
> > > + * device owner of the best migration destination. e.g.,
> > > device0/vm0
> > > + * has a page fault, but we have determined the best
> > > placement of
> > > + * the fault address should be on device1, we should set
> > > below to
> > > + * device1 instead of device0.
> > > + */
> > > + hmm_range.dev_private_owner = vm->xe;
> > > +
> > > + while (true) {
> > > + hmm_range.notifier_seq =
> > > mmu_interval_read_begin(&userptr->notifier);
> > > + ret = hmm_range_fault(&hmm_range);
> > > + if (time_after(jiffies, timeout))
> > > + break;
> > > +
> > > + if (ret == -EBUSY)
> > > + continue;
> > > + break;
> > > + }
> > > +
> > > + if (in_kthread) {
> > > + kthread_unuse_mm(userptr->notifier.mm);
> > > + mmput(userptr->notifier.mm);
> > > + }
> > > +
> > > + if (ret)
> > > + goto free_pfns;
> > > +
> > > + ret = build_sg(vm->xe, &hmm_range, &userptr->sgt, write);
> > > + if (ret)
> > > + goto free_pfns;
> > > +
> > > + xe_mark_range_accessed(&hmm_range, write);
> > > + userptr->sg = &userptr->sgt;
> > > + userptr->notifier_seq = hmm_range.notifier_seq;
> > > +
> > > +free_pfns:
> > > + kvfree(pfns);
> > > + return ret;
> > > +}
> > > +
> > > diff --git a/drivers/gpu/drm/xe/xe_hmm.h
> > > b/drivers/gpu/drm/xe/xe_hmm.h
> > > new file mode 100644
> > > index 000000000000..fa5ddc11f10b
> > > --- /dev/null
> > > +++ b/drivers/gpu/drm/xe/xe_hmm.h
> > > @@ -0,0 +1,10 @@
> > > +// SPDX-License-Identifier: MIT
> > > +/*
> > > + * Copyright © 2024 Intel Corporation
> > > + */
> > > +
> > > +#include <linux/types.h>
> > > +
> > > +struct xe_userptr_vma;
> > > +
> > > +int xe_userptr_populate_range(struct xe_userptr_vma *uvma);
> >
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