Commit de293938 authored by Jens Axboe's avatar Jens Axboe
Browse files

io_uring: improve registered buffer accounting for huge pages 



io_uring does account any registered buffer as pinned/locked memory, and
checks limit and fails if the given user doesn't have a big enough limit
to register the ranges specified. However, if huge pages are used, we
are potentially under-accounting the memory in terms of what gets pinned
on the vm side.

This patch rectifies that, by ensuring that we account the full size of
a compound page, regardless of how much of it is being registered. Huge
pages are not accounted mulitple times - if multiple sections of a huge
page is registered, then the page is only accounted once.

Reported-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 14db8411

fs/io_uring.c

+80 −10
Original line number Diff line number Diff line
@@ -190,6 +190,7 @@ struct io_mapped_ubuf { 
	size_t		len;

	struct		bio_vec *bvec;

	unsigned int	nr_bvecs;

	unsigned long	acct_pages;

};



struct fixed_file_table {
@@ -8002,7 +8003,8 @@ static int io_sqe_buffer_unregister(struct io_ring_ctx *ctx) 
		for (j = 0; j < imu->nr_bvecs; j++)

			unpin_user_page(imu->bvec[j].bv_page);



		io_unaccount_mem(ctx, imu->nr_bvecs, ACCT_PINNED);

		if (imu->acct_pages)

			io_unaccount_mem(ctx, imu->acct_pages, ACCT_PINNED);

		kvfree(imu->bvec);

		imu->nr_bvecs = 0;

	}
@@ -8038,11 +8040,80 @@ static int io_copy_iov(struct io_ring_ctx *ctx, struct iovec *dst, 
	return 0;

}



/*

 * Not super efficient, but this is just a registration time. And we do cache

 * the last compound head, so generally we'll only do a full search if we don't

 * match that one.

 *

 * We check if the given compound head page has already been accounted, to

 * avoid double accounting it. This allows us to account the full size of the

 * page, not just the constituent pages of a huge page.

 */

static bool headpage_already_acct(struct io_ring_ctx *ctx, struct page **pages,

				  int nr_pages, struct page *hpage)

{

	int i, j;



	/* check current page array */

	for (i = 0; i < nr_pages; i++) {

		if (!PageCompound(pages[i]))

			continue;

		if (compound_head(pages[i]) == hpage)

			return true;

	}



	/* check previously registered pages */

	for (i = 0; i < ctx->nr_user_bufs; i++) {

		struct io_mapped_ubuf *imu = &ctx->user_bufs[i];



		for (j = 0; j < imu->nr_bvecs; j++) {

			if (!PageCompound(imu->bvec[j].bv_page))

				continue;

			if (compound_head(imu->bvec[j].bv_page) == hpage)

				return true;

		}

	}



	return false;

}



static int io_buffer_account_pin(struct io_ring_ctx *ctx, struct page **pages,

				 int nr_pages, struct io_mapped_ubuf *imu,

				 struct page **last_hpage)

{

	int i, ret;



	for (i = 0; i < nr_pages; i++) {

		if (!PageCompound(pages[i])) {

			imu->acct_pages++;

		} else {

			struct page *hpage;



			hpage = compound_head(pages[i]);

			if (hpage == *last_hpage)

				continue;

			*last_hpage = hpage;

			if (headpage_already_acct(ctx, pages, i, hpage))

				continue;

			imu->acct_pages += page_size(hpage) >> PAGE_SHIFT;

		}

	}



	if (!imu->acct_pages)

		return 0;



	ret = io_account_mem(ctx, imu->acct_pages, ACCT_PINNED);

	if (ret)

		imu->acct_pages = 0;

	return ret;

}



static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,

				  unsigned nr_args)

{

	struct vm_area_struct **vmas = NULL;

	struct page **pages = NULL;

	struct page *last_hpage = NULL;

	int i, j, got_pages = 0;

	int ret = -EINVAL;
@@ -8085,10 +8156,6 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg, 
		start = ubuf >> PAGE_SHIFT;

		nr_pages = end - start;



		ret = io_account_mem(ctx, nr_pages, ACCT_PINNED);

		if (ret)

			goto err;



		ret = 0;

		if (!pages || nr_pages > got_pages) {

			kvfree(vmas);
@@ -8100,7 +8167,6 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg, 
					GFP_KERNEL);

			if (!pages || !vmas) {

				ret = -ENOMEM;

				io_unaccount_mem(ctx, nr_pages, ACCT_PINNED);

				goto err;

			}

			got_pages = nr_pages;
@@ -8109,10 +8175,8 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg, 
		imu->bvec = kvmalloc_array(nr_pages, sizeof(struct bio_vec),

						GFP_KERNEL);

		ret = -ENOMEM;

		if (!imu->bvec) {

			io_unaccount_mem(ctx, nr_pages, ACCT_PINNED);

		if (!imu->bvec)

			goto err;

		}



		ret = 0;

		mmap_read_lock(current->mm);
@@ -8141,7 +8205,13 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg, 
			 */

			if (pret > 0)

				unpin_user_pages(pages, pret);

			io_unaccount_mem(ctx, nr_pages, ACCT_PINNED);

			kvfree(imu->bvec);

			goto err;

		}



		ret = io_buffer_account_pin(ctx, pages, pret, imu, &last_hpage);

		if (ret) {

			unpin_user_pages(pages, pret);

			kvfree(imu->bvec);

			goto err;

		}

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