drm/xe: Introduce helper to populate userptr

Introduce a helper function xe_userptr_populate_range to populate
a userptr range. This functions calls hmm_range_fault to read
CPU page tables and populate all pfns/pages of this virtual address
range. For system memory page, dma-mapping is performed
to get a dma-address which can be used later for GPU to access pages.

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)
v2: Remove device private page support. Only support system
    pages for now. use dma-map-sg rather than dma-map-page (Matt/Thomas)
v3: Address review comments:
    Squash patch "drm/xe: Introduce a helper to free sg table" to current
    patch (Matt)
    start and end addresses are already page aligned (Matt)
    Do mmap_read_lock and mmap_read_unlock for hmm_range_fault incase of
    non system allocator call. (Matt)
    Drop kthread_use_mm and kthread_unuse_mm. (Matt)
    No need of kernel-doc for static functions.(Matt)
    Modify function names. (Matt)
    Free sgtable incase of dma_map_sgtable failure.(Matt)
    Modify loop for hmm_range_fault.(Matt)
v4: Remove the dummy function for xe_hmm_userptr_populate_range
    since CONFIG_HMM_MIRROR is needed. (Matt)
    Change variable names start/end to userptr_start/userptr_end.(Matt)
v5: Remove device private page support info from commit message. Since
    the patch doesn't support device page handling. (Thomas)
Signed-off-by: Oak Zeng <oak.zeng@intel.com>
Co-developed-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@intel.com>
Cc: Brian Welty <brian.welty@intel.com>
Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240412095237.1048599-2-himal.prasad.ghimiray@intel.com

drivers/gpu/drm/xe/Kconfig

@@ -41,6 +41,7 @@ config DRM_XE
 	select MMU_NOTIFIER
 	select WANT_DEV_COREDUMP
 	select AUXILIARY_BUS
+	select HMM_MIRROR
 	help
 	  Experimental driver for Intel Xe series GPUs
 

drivers/gpu/drm/xe/Makefile

@@ -147,6 +147,8 @@ xe-y += xe_bb.o \
 	xe_wa.o \
 	xe_wopcm.o
 
+xe-$(CONFIG_HMM_MIRROR) += xe_hmm.o
+
 # graphics hardware monitoring (HWMON) support
 xe-$(CONFIG_HWMON) += xe_hwmon.o
 

drivers/gpu/drm/xe/xe_hmm.c

+// SPDX-License-Identifier: MIT
+/*
+ * Copyright © 2024 Intel Corporation
+ */
+
+#include <linux/scatterlist.h>
+#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_vm.h"
+#include "xe_bo.h"
+
+static u64 xe_npages_in_range(unsigned long start, unsigned long end)
+{
+	return (end - start) >> PAGE_SHIFT;
+}
+
+/*
+ * 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 = xe_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);
+	}
+}
+
+/*
+ * xe_build_sg() - build a scatter gather table for all the physical pages/pfn
+ * in a hmm_range. dma-map pages if necessary. 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 purpose of efficiently
+ * programming 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.
+ *
+ * FIXME: This function currently only support pages in system
+ * memory. 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. This is TBD.
+ *
+ * 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 xe_build_sg(struct xe_device *xe, struct hmm_range *range,
+		       struct sg_table *st, bool write)
+{
+	struct device *dev = xe->drm.dev;
+	struct page **pages;
+	u64 i, npages;
+	int ret;
+
+	npages = xe_npages_in_range(range->start, range->end);
+	pages = kvmalloc_array(npages, sizeof(*pages), GFP_KERNEL);
+	if (!pages)
+		return -ENOMEM;
+
+	for (i = 0; i < npages; i++) {
+		pages[i] = hmm_pfn_to_page(range->hmm_pfns[i]);
+		xe_assert(xe, !is_device_private_page(pages[i]));
+	}
+
+	ret = sg_alloc_table_from_pages_segment(st, pages, npages, 0, npages << PAGE_SHIFT,
+						xe_sg_segment_size(dev), GFP_KERNEL);
+	if (ret)
+		goto free_pages;
+
+	ret = dma_map_sgtable(dev, st, write ? DMA_BIDIRECTIONAL : DMA_TO_DEVICE,
+			      DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_NO_KERNEL_MAPPING);
+	if (ret) {
+		sg_free_table(st);
+		st = NULL;
+	}
+
+free_pages:
+	kvfree(pages);
+	return ret;
+}
+
+/*
+ * xe_hmm_userptr_free_sg() - Free the scatter gather table of userptr
+ *
+ * @uvma: the userptr vma which hold the scatter gather table
+ *
+ * With function xe_userptr_populate_range, we allocate storage of
+ * the userptr sg table. This is a helper function to free this
+ * sg table, and dma unmap the address in the table.
+ */
+void xe_hmm_userptr_free_sg(struct xe_userptr_vma *uvma)
+{
+	struct xe_userptr *userptr = &uvma->userptr;
+	struct xe_vma *vma = &uvma->vma;
+	bool write = !xe_vma_read_only(vma);
+	struct xe_vm *vm = xe_vma_vm(vma);
+	struct xe_device *xe = vm->xe;
+	struct device *dev = xe->drm.dev;
+
+	xe_assert(xe, userptr->sg);
+	dma_unmap_sgtable(dev, userptr->sg,
+			  write ? DMA_BIDIRECTIONAL : DMA_TO_DEVICE, 0);
+
+	sg_free_table(userptr->sg);
+	userptr->sg = NULL;
+}
+
+/**
+ * xe_hmm_userptr_populate_range() - Populate physical pages of a virtual
+ * address range
+ *
+ * @uvma: userptr vma which has information of the range to populate.
+ * @is_mm_mmap_locked: True if mmap_read_lock is already acquired by caller.
+ *
+ * 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_hmm_userptr_populate_range(struct xe_userptr_vma *uvma,
+				  bool is_mm_mmap_locked)
+{
+	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 userptr_start = xe_vma_userptr(vma);
+	u64 userptr_end = userptr_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);
+	unsigned long notifier_seq;
+	u64 npages;
+	int ret;
+
+	userptr = &uvma->userptr;
+
+	if (is_mm_mmap_locked)
+		mmap_assert_locked(userptr->notifier.mm);
+
+	if (vma->gpuva.flags & XE_VMA_DESTROYED)
+		return 0;
+
+	notifier_seq = mmu_interval_read_begin(&userptr->notifier);
+	if (notifier_seq == userptr->notifier_seq)
+		return 0;
+
+	if (userptr->sg)
+		xe_hmm_userptr_free_sg(uvma);
+
+	npages = xe_npages_in_range(userptr_start, userptr_end);
+	pfns = kvmalloc_array(npages, sizeof(*pfns), GFP_KERNEL);
+	if (unlikely(!pfns))
+		return -ENOMEM;
+
+	if (write)
+		flags |= HMM_PFN_REQ_WRITE;
+
+	if (!mmget_not_zero(userptr->notifier.mm)) {
+		ret = -EFAULT;
+		goto free_pfns;
+	}
+
+	hmm_range.default_flags = flags;
+	hmm_range.hmm_pfns = pfns;
+	hmm_range.notifier = &userptr->notifier;
+	hmm_range.start = userptr_start;
+	hmm_range.end = userptr_end;
+	hmm_range.dev_private_owner = vm->xe;
+
+	while (true) {
+		hmm_range.notifier_seq = mmu_interval_read_begin(&userptr->notifier);
+
+		if (!is_mm_mmap_locked)
+			mmap_read_lock(userptr->notifier.mm);
+
+		ret = hmm_range_fault(&hmm_range);
+
+		if (!is_mm_mmap_locked)
+			mmap_read_unlock(userptr->notifier.mm);
+
+		if (ret == -EBUSY) {
+			if (time_after(jiffies, timeout))
+				break;
+
+			continue;
+		}
+		break;
+	}
+
+	mmput(userptr->notifier.mm);
+
+	if (ret)
+		goto free_pfns;
+
+	ret = xe_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;
+}
+

drivers/gpu/drm/xe/xe_hmm.h

+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright © 2024 Intel Corporation
+ */
+
+#include <linux/types.h>
+
+struct xe_userptr_vma;
+
+int xe_hmm_userptr_populate_range(struct xe_userptr_vma *uvma, bool is_mm_mmap_locked);
+void xe_hmm_userptr_free_sg(struct xe_userptr_vma *uvma);