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d77e59a8fc
Initialising the tags and setting PG_mte_tagged flag for a page can race between multiple set_pte_at() on shared pages or setting the stage 2 pte via user_mem_abort(). Introduce a new PG_mte_lock flag as PG_arch_3 and set it before attempting page initialisation. Given that PG_mte_tagged is never cleared for a page, consider setting this flag to mean page unlocked and wait on this bit with acquire semantics if the page is locked: - try_page_mte_tagging() - lock the page for tagging, return true if it can be tagged, false if already tagged. No acquire semantics if it returns true (PG_mte_tagged not set) as there is no serialisation with a previous set_page_mte_tagged(). - set_page_mte_tagged() - set PG_mte_tagged with release semantics. The two-bit locking is based on Peter Collingbourne's idea. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Peter Collingbourne <pcc@google.com> Reviewed-by: Steven Price <steven.price@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Marc Zyngier <maz@kernel.org> Cc: Peter Collingbourne <pcc@google.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Signed-off-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20221104011041.290951-6-pcc@google.com
84 lines
1.8 KiB
C
84 lines
1.8 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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#include <linux/pagemap.h>
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#include <linux/xarray.h>
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#include <linux/slab.h>
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#include <linux/swap.h>
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#include <linux/swapops.h>
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#include <asm/mte.h>
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static DEFINE_XARRAY(mte_pages);
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void *mte_allocate_tag_storage(void)
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{
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/* tags granule is 16 bytes, 2 tags stored per byte */
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return kmalloc(MTE_PAGE_TAG_STORAGE, GFP_KERNEL);
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}
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void mte_free_tag_storage(char *storage)
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{
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kfree(storage);
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}
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int mte_save_tags(struct page *page)
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{
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void *tag_storage, *ret;
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if (!page_mte_tagged(page))
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return 0;
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tag_storage = mte_allocate_tag_storage();
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if (!tag_storage)
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return -ENOMEM;
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mte_save_page_tags(page_address(page), tag_storage);
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/* page_private contains the swap entry.val set in do_swap_page */
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ret = xa_store(&mte_pages, page_private(page), tag_storage, GFP_KERNEL);
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if (WARN(xa_is_err(ret), "Failed to store MTE tags")) {
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mte_free_tag_storage(tag_storage);
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return xa_err(ret);
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} else if (ret) {
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/* Entry is being replaced, free the old entry */
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mte_free_tag_storage(ret);
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}
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return 0;
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}
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void mte_restore_tags(swp_entry_t entry, struct page *page)
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{
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void *tags = xa_load(&mte_pages, entry.val);
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if (!tags)
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return;
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if (try_page_mte_tagging(page)) {
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mte_restore_page_tags(page_address(page), tags);
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set_page_mte_tagged(page);
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}
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}
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void mte_invalidate_tags(int type, pgoff_t offset)
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{
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swp_entry_t entry = swp_entry(type, offset);
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void *tags = xa_erase(&mte_pages, entry.val);
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mte_free_tag_storage(tags);
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}
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void mte_invalidate_tags_area(int type)
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{
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swp_entry_t entry = swp_entry(type, 0);
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swp_entry_t last_entry = swp_entry(type + 1, 0);
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void *tags;
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XA_STATE(xa_state, &mte_pages, entry.val);
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xa_lock(&mte_pages);
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xas_for_each(&xa_state, tags, last_entry.val - 1) {
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__xa_erase(&mte_pages, xa_state.xa_index);
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mte_free_tag_storage(tags);
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}
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xa_unlock(&mte_pages);
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}
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