vfio: Move iova_bitmap into iommufd

Both VFIO and IOMMUFD will need iova bitmap for storing dirties and walking
the user bitmaps, so move to the common dependency into IOMMUFD.  In doing
so, create the symbol IOMMUFD_DRIVER which designates the builtin code that
will be used by drivers when selected. Today this means MLX5_VFIO_PCI and
PDS_VFIO_PCI. IOMMU drivers will do the same (in future patches) when
supporting dirty tracking and select IOMMUFD_DRIVER accordingly.

Given that the symbol maybe be disabled, add header definitions in
iova_bitmap.h for when IOMMUFD_DRIVER=n

Link: https://lore.kernel.org/r/20231024135109.73787-3-joao.m.martins@oracle.com
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Brett Creeley <brett.creeley@amd.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

2 files changed, 427 insertions, 0 deletions

diff --git a/drivers/iommu/iommufd/Makefile b/drivers/iommu/iommufd/Makefile
index 8aeba81800c5..34b446146961 100644
--- a/drivers/iommu/iommufd/Makefile
+++ b/drivers/iommu/iommufd/Makefile
@@ -11,3 +11,4 @@ iommufd-y := \
 iommufd-$(CONFIG_IOMMUFD_TEST) += selftest.o
 
 obj-$(CONFIG_IOMMUFD) += iommufd.o
+obj-$(CONFIG_IOMMUFD_DRIVER) += iova_bitmap.o
diff --git a/drivers/iommu/iommufd/iova_bitmap.c b/drivers/iommu/iommufd/iova_bitmap.c
new file mode 100644
index 000000000000..f54b56388e00
--- /dev/null
+++ b/drivers/iommu/iommufd/iova_bitmap.c
@@ -0,0 +1,426 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2022, Oracle and/or its affiliates.
+ * Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved
+ */
+#include <linux/iova_bitmap.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/highmem.h>
+
+#define BITS_PER_PAGE (PAGE_SIZE * BITS_PER_BYTE)
+
+/*
+ * struct iova_bitmap_map - A bitmap representing an IOVA range
+ *
+ * Main data structure for tracking mapped user pages of bitmap data.
+ *
+ * For example, for something recording dirty IOVAs, it will be provided a
+ * struct iova_bitmap structure, as a general structure for iterating the
+ * total IOVA range. The struct iova_bitmap_map, though, represents the
+ * subset of said IOVA space that is pinned by its parent structure (struct
+ * iova_bitmap).
+ *
+ * The user does not need to exact location of the bits in the bitmap.
+ * From user perspective the only API available is iova_bitmap_set() which
+ * records the IOVA *range* in the bitmap by setting the corresponding
+ * bits.
+ *
+ * The bitmap is an array of u64 whereas each bit represents an IOVA of
+ * range of (1 << pgshift). Thus formula for the bitmap data to be set is:
+ *
+ *   data[(iova / page_size) / 64] & (1ULL << (iova % 64))
+ */
+struct iova_bitmap_map {
+	/* base IOVA representing bit 0 of the first page */
+	unsigned long iova;
+
+	/* page size order that each bit granules to */
+	unsigned long pgshift;
+
+	/* page offset of the first user page pinned */
+	unsigned long pgoff;
+
+	/* number of pages pinned */
+	unsigned long npages;
+
+	/* pinned pages representing the bitmap data */
+	struct page **pages;
+};
+
+/*
+ * struct iova_bitmap - The IOVA bitmap object
+ *
+ * Main data structure for iterating over the bitmap data.
+ *
+ * Abstracts the pinning work and iterates in IOVA ranges.
+ * It uses a windowing scheme and pins the bitmap in relatively
+ * big ranges e.g.
+ *
+ * The bitmap object uses one base page to store all the pinned pages
+ * pointers related to the bitmap. For sizeof(struct page*) == 8 it stores
+ * 512 struct page pointers which, if the base page size is 4K, it means
+ * 2M of bitmap data is pinned at a time. If the iova_bitmap page size is
+ * also 4K then the range window to iterate is 64G.
+ *
+ * For example iterating on a total IOVA range of 4G..128G, it will walk
+ * through this set of ranges:
+ *
+ *    4G  -  68G-1 (64G)
+ *    68G - 128G-1 (64G)
+ *
+ * An example of the APIs on how to use/iterate over the IOVA bitmap:
+ *
+ *   bitmap = iova_bitmap_alloc(iova, length, page_size, data);
+ *   if (IS_ERR(bitmap))
+ *       return PTR_ERR(bitmap);
+ *
+ *   ret = iova_bitmap_for_each(bitmap, arg, dirty_reporter_fn);
+ *
+ *   iova_bitmap_free(bitmap);
+ *
+ * Each iteration of the @dirty_reporter_fn is called with a unique @iova
+ * and @length argument, indicating the current range available through the
+ * iova_bitmap. The @dirty_reporter_fn uses iova_bitmap_set() to mark dirty
+ * areas (@iova_length) within that provided range, as following:
+ *
+ *   iova_bitmap_set(bitmap, iova, iova_length);
+ *
+ * The internals of the object uses an index @mapped_base_index that indexes
+ * which u64 word of the bitmap is mapped, up to @mapped_total_index.
+ * Those keep being incremented until @mapped_total_index is reached while
+ * mapping up to PAGE_SIZE / sizeof(struct page*) maximum of pages.
+ *
+ * The IOVA bitmap is usually located on what tracks DMA mapped ranges or
+ * some form of IOVA range tracking that co-relates to the user passed
+ * bitmap.
+ */
+struct iova_bitmap {
+	/* IOVA range representing the currently mapped bitmap data */
+	struct iova_bitmap_map mapped;
+
+	/* userspace address of the bitmap */
+	u64 __user *bitmap;
+
+	/* u64 index that @mapped points to */
+	unsigned long mapped_base_index;
+
+	/* how many u64 can we walk in total */
+	unsigned long mapped_total_index;
+
+	/* base IOVA of the whole bitmap */
+	unsigned long iova;
+
+	/* length of the IOVA range for the whole bitmap */
+	size_t length;
+};
+
+/*
+ * Converts a relative IOVA to a bitmap index.
+ * This function provides the index into the u64 array (bitmap::bitmap)
+ * for a given IOVA offset.
+ * Relative IOVA means relative to the bitmap::mapped base IOVA
+ * (stored in mapped::iova). All computations in this file are done using
+ * relative IOVAs and thus avoid an extra subtraction against mapped::iova.
+ * The user API iova_bitmap_set() always uses a regular absolute IOVAs.
+ */
+static unsigned long iova_bitmap_offset_to_index(struct iova_bitmap *bitmap,
+						 unsigned long iova)
+{
+	unsigned long pgsize = 1 << bitmap->mapped.pgshift;
+
+	return iova / (BITS_PER_TYPE(*bitmap->bitmap) * pgsize);
+}
+
+/*
+ * Converts a bitmap index to a *relative* IOVA.
+ */
+static unsigned long iova_bitmap_index_to_offset(struct iova_bitmap *bitmap,
+						 unsigned long index)
+{
+	unsigned long pgshift = bitmap->mapped.pgshift;
+
+	return (index * BITS_PER_TYPE(*bitmap->bitmap)) << pgshift;
+}
+
+/*
+ * Returns the base IOVA of the mapped range.
+ */
+static unsigned long iova_bitmap_mapped_iova(struct iova_bitmap *bitmap)
+{
+	unsigned long skip = bitmap->mapped_base_index;
+
+	return bitmap->iova + iova_bitmap_index_to_offset(bitmap, skip);
+}
+
+/*
+ * Pins the bitmap user pages for the current range window.
+ * This is internal to IOVA bitmap and called when advancing the
+ * index (@mapped_base_index) or allocating the bitmap.
+ */
+static int iova_bitmap_get(struct iova_bitmap *bitmap)
+{
+	struct iova_bitmap_map *mapped = &bitmap->mapped;
+	unsigned long npages;
+	u64 __user *addr;
+	long ret;
+
+	/*
+	 * @mapped_base_index is the index of the currently mapped u64 words
+	 * that we have access. Anything before @mapped_base_index is not
+	 * mapped. The range @mapped_base_index .. @mapped_total_index-1 is
+	 * mapped but capped at a maximum number of pages.
+	 */
+	npages = DIV_ROUND_UP((bitmap->mapped_total_index -
+			       bitmap->mapped_base_index) *
+			       sizeof(*bitmap->bitmap), PAGE_SIZE);
+
+	/*
+	 * We always cap at max number of 'struct page' a base page can fit.
+	 * This is, for example, on x86 means 2M of bitmap data max.
+	 */
+	npages = min(npages,  PAGE_SIZE / sizeof(struct page *));
+
+	/*
+	 * Bitmap address to be pinned is calculated via pointer arithmetic
+	 * with bitmap u64 word index.
+	 */
+	addr = bitmap->bitmap + bitmap->mapped_base_index;
+
+	ret = pin_user_pages_fast((unsigned long)addr, npages,
+				  FOLL_WRITE, mapped->pages);
+	if (ret <= 0)
+		return -EFAULT;
+
+	mapped->npages = (unsigned long)ret;
+	/* Base IOVA where @pages point to i.e. bit 0 of the first page */
+	mapped->iova = iova_bitmap_mapped_iova(bitmap);
+
+	/*
+	 * offset of the page where pinned pages bit 0 is located.
+	 * This handles the case where the bitmap is not PAGE_SIZE
+	 * aligned.
+	 */
+	mapped->pgoff = offset_in_page(addr);
+	return 0;
+}
+
+/*
+ * Unpins the bitmap user pages and clears @npages
+ * (un)pinning is abstracted from API user and it's done when advancing
+ * the index or freeing the bitmap.
+ */
+static void iova_bitmap_put(struct iova_bitmap *bitmap)
+{
+	struct iova_bitmap_map *mapped = &bitmap->mapped;
+
+	if (mapped->npages) {
+		unpin_user_pages(mapped->pages, mapped->npages);
+		mapped->npages = 0;
+	}
+}
+
+/**
+ * iova_bitmap_alloc() - Allocates an IOVA bitmap object
+ * @iova: Start address of the IOVA range
+ * @length: Length of the IOVA range
+ * @page_size: Page size of the IOVA bitmap. It defines what each bit
+ *             granularity represents
+ * @data: Userspace address of the bitmap
+ *
+ * Allocates an IOVA object and initializes all its fields including the
+ * first user pages of @data.
+ *
+ * Return: A pointer to a newly allocated struct iova_bitmap
+ * or ERR_PTR() on error.
+ */
+struct iova_bitmap *iova_bitmap_alloc(unsigned long iova, size_t length,
+				      unsigned long page_size, u64 __user *data)
+{
+	struct iova_bitmap_map *mapped;
+	struct iova_bitmap *bitmap;
+	int rc;
+
+	bitmap = kzalloc(sizeof(*bitmap), GFP_KERNEL);
+	if (!bitmap)
+		return ERR_PTR(-ENOMEM);
+
+	mapped = &bitmap->mapped;
+	mapped->pgshift = __ffs(page_size);
+	bitmap->bitmap = data;
+	bitmap->mapped_total_index =
+		iova_bitmap_offset_to_index(bitmap, length - 1) + 1;
+	bitmap->iova = iova;
+	bitmap->length = length;
+	mapped->iova = iova;
+	mapped->pages = (struct page **)__get_free_page(GFP_KERNEL);
+	if (!mapped->pages) {
+		rc = -ENOMEM;
+		goto err;
+	}
+
+	rc = iova_bitmap_get(bitmap);
+	if (rc)
+		goto err;
+	return bitmap;
+
+err:
+	iova_bitmap_free(bitmap);
+	return ERR_PTR(rc);
+}
+EXPORT_SYMBOL_GPL(iova_bitmap_alloc);
+
+/**
+ * iova_bitmap_free() - Frees an IOVA bitmap object
+ * @bitmap: IOVA bitmap to free
+ *
+ * It unpins and releases pages array memory and clears any leftover
+ * state.
+ */
+void iova_bitmap_free(struct iova_bitmap *bitmap)
+{
+	struct iova_bitmap_map *mapped = &bitmap->mapped;
+
+	iova_bitmap_put(bitmap);
+
+	if (mapped->pages) {
+		free_page((unsigned long)mapped->pages);
+		mapped->pages = NULL;
+	}
+
+	kfree(bitmap);
+}
+EXPORT_SYMBOL_GPL(iova_bitmap_free);
+
+/*
+ * Returns the remaining bitmap indexes from mapped_total_index to process for
+ * the currently pinned bitmap pages.
+ */
+static unsigned long iova_bitmap_mapped_remaining(struct iova_bitmap *bitmap)
+{
+	unsigned long remaining, bytes;
+
+	bytes = (bitmap->mapped.npages << PAGE_SHIFT) - bitmap->mapped.pgoff;
+
+	remaining = bitmap->mapped_total_index - bitmap->mapped_base_index;
+	remaining = min_t(unsigned long, remaining,
+			  bytes / sizeof(*bitmap->bitmap));
+
+	return remaining;
+}
+
+/*
+ * Returns the length of the mapped IOVA range.
+ */
+static unsigned long iova_bitmap_mapped_length(struct iova_bitmap *bitmap)
+{
+	unsigned long max_iova = bitmap->iova + bitmap->length - 1;
+	unsigned long iova = iova_bitmap_mapped_iova(bitmap);
+	unsigned long remaining;
+
+	/*
+	 * iova_bitmap_mapped_remaining() returns a number of indexes which
+	 * when converted to IOVA gives us a max length that the bitmap
+	 * pinned data can cover. Afterwards, that is capped to
+	 * only cover the IOVA range in @bitmap::iova .. @bitmap::length.
+	 */
+	remaining = iova_bitmap_index_to_offset(bitmap,
+			iova_bitmap_mapped_remaining(bitmap));
+
+	if (iova + remaining - 1 > max_iova)
+		remaining -= ((iova + remaining - 1) - max_iova);
+
+	return remaining;
+}
+
+/*
+ * Returns true if there's not more data to iterate.
+ */
+static bool iova_bitmap_done(struct iova_bitmap *bitmap)
+{
+	return bitmap->mapped_base_index >= bitmap->mapped_total_index;
+}
+
+/*
+ * Advances to the next range, releases the current pinned
+ * pages and pins the next set of bitmap pages.
+ * Returns 0 on success or otherwise errno.
+ */
+static int iova_bitmap_advance(struct iova_bitmap *bitmap)
+{
+	unsigned long iova = iova_bitmap_mapped_length(bitmap) - 1;
+	unsigned long count = iova_bitmap_offset_to_index(bitmap, iova) + 1;
+
+	bitmap->mapped_base_index += count;
+
+	iova_bitmap_put(bitmap);
+	if (iova_bitmap_done(bitmap))
+		return 0;
+
+	/* When advancing the index we pin the next set of bitmap pages */
+	return iova_bitmap_get(bitmap);
+}
+
+/**
+ * iova_bitmap_for_each() - Iterates over the bitmap
+ * @bitmap: IOVA bitmap to iterate
+ * @opaque: Additional argument to pass to the callback
+ * @fn: Function that gets called for each IOVA range
+ *
+ * Helper function to iterate over bitmap data representing a portion of IOVA
+ * space. It hides the complexity of iterating bitmaps and translating the
+ * mapped bitmap user pages into IOVA ranges to process.
+ *
+ * Return: 0 on success, and an error on failure either upon
+ * iteration or when the callback returns an error.
+ */
+int iova_bitmap_for_each(struct iova_bitmap *bitmap, void *opaque,
+			 iova_bitmap_fn_t fn)
+{
+	int ret = 0;
+
+	for (; !iova_bitmap_done(bitmap) && !ret;
+	     ret = iova_bitmap_advance(bitmap)) {
+		ret = fn(bitmap, iova_bitmap_mapped_iova(bitmap),
+			 iova_bitmap_mapped_length(bitmap), opaque);
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iova_bitmap_for_each);
+
+/**
+ * iova_bitmap_set() - Records an IOVA range in bitmap
+ * @bitmap: IOVA bitmap
+ * @iova: IOVA to start
+ * @length: IOVA range length
+ *
+ * Set the bits corresponding to the range [iova .. iova+length-1] in
+ * the user bitmap.
+ *
+ */
+void iova_bitmap_set(struct iova_bitmap *bitmap,
+		     unsigned long iova, size_t length)
+{
+	struct iova_bitmap_map *mapped = &bitmap->mapped;
+	unsigned long cur_bit = ((iova - mapped->iova) >>
+			mapped->pgshift) + mapped->pgoff * BITS_PER_BYTE;
+	unsigned long last_bit = (((iova + length - 1) - mapped->iova) >>
+			mapped->pgshift) + mapped->pgoff * BITS_PER_BYTE;
+
+	do {
+		unsigned int page_idx = cur_bit / BITS_PER_PAGE;
+		unsigned int offset = cur_bit % BITS_PER_PAGE;
+		unsigned int nbits = min(BITS_PER_PAGE - offset,
+					 last_bit - cur_bit + 1);
+		void *kaddr;
+
+		kaddr = kmap_local_page(mapped->pages[page_idx]);
+		bitmap_set(kaddr, offset, nbits);
+		kunmap_local(kaddr);
+		cur_bit += nbits;
+	} while (cur_bit <= last_bit);
+}
+EXPORT_SYMBOL_GPL(iova_bitmap_set);