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The new facility adds a bunch of wrappers that abstract how an IOVA range
is represented in a bitmap that is granulated by a given page_size. So it
translates all the lifting of dealing with user pointers into its
corresponding kernel addresses backing said user memory into doing finally
the (non-atomic) bitmap ops to change various bits.
The formula for the bitmap is:
data[(iova / page_size) / 64] & (1ULL << (iova % 64))
Where 64 is the number of bits in a unsigned long (depending on arch)
It introduces an IOVA iterator that uses a windowing scheme to minimize the
pinning overhead, as opposed to pinning it on demand 4K at a time. Assuming
a 4K kernel page and 4K requested page size, we can use a single kernel
page to hold 512 page pointers, mapping 2M of bitmap, representing 64G of
IOVA space.
An example usage of these helpers for a given @base_iova, @page_size,
@length and __user @data:
bitmap = iova_bitmap_alloc(base_iova, page_size, length, data);
if (IS_ERR(bitmap))
return -ENOMEM;
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 facility is intended to be used for user bitmaps representing dirtied
IOVAs by IOMMU (via IOMMUFD) and PCI Devices (via vfio-pci).
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://lore.kernel.org/r/20220908183448.195262-5-yishaih@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
26 lines
771 B
C
26 lines
771 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Copyright (c) 2022, Oracle and/or its affiliates.
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* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved
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*/
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#ifndef _IOVA_BITMAP_H_
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#define _IOVA_BITMAP_H_
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#include <linux/types.h>
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struct iova_bitmap;
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typedef int (*iova_bitmap_fn_t)(struct iova_bitmap *bitmap,
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unsigned long iova, size_t length,
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void *opaque);
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struct iova_bitmap *iova_bitmap_alloc(unsigned long iova, size_t length,
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unsigned long page_size,
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u64 __user *data);
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void iova_bitmap_free(struct iova_bitmap *bitmap);
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int iova_bitmap_for_each(struct iova_bitmap *bitmap, void *opaque,
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iova_bitmap_fn_t fn);
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void iova_bitmap_set(struct iova_bitmap *bitmap,
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unsigned long iova, size_t length);
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#endif
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