[PATCH RFC v2 16/27] arm64: mte: Manage tag storage on page allocation

Alexandru Elisei
2023-11-19T16:59:41Z

Reserve tag storage for a tagged page by migrating the contents of the tag
storage (if in use for data) and removing the tag storage pages from the
page allocator by calling alloc_contig_range().

When all the associated tagged pages have been freed, return the tag
storage pages back to the page allocator, where they can be used again for
data allocations.

Tag storage pages cannot be tagged, so disallow allocations from
MIGRATE_CMA when the allocation is tagged.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
---
arch/arm64/include/asm/mte.h | 16 +-
arch/arm64/include/asm/mte_tag_storage.h | 45 +++++
arch/arm64/include/asm/pgtable.h | 27 +++
arch/arm64/kernel/mte_tag_storage.c | 241 +++++++++++++++++++++++
fs/proc/page.c | 1 +
include/linux/kernel-page-flags.h | 1 +
include/linux/page-flags.h | 1 +
include/trace/events/mmflags.h | 3 +-
mm/huge_memory.c | 1 +
9 files changed, 333 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index 8034695b3dd7..6457b7899207 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -40,12 +40,24 @@ void mte_free_tag_buf(void *buf);
#ifdef CONFIG_ARM64_MTE

/* track which pages have valid allocation tags */
-#define PG_mte_tagged PG_arch_2
+#define PG_mte_tagged PG_arch_2
/* simple lock to avoid multiple threads tagging the same page */
-#define PG_mte_lock PG_arch_3
+#define PG_mte_lock PG_arch_3
+/* Track if a tagged page has tag storage reserved */
+#define PG_tag_storage_reserved PG_arch_4
+
+#ifdef CONFIG_ARM64_MTE_TAG_STORAGE
+DECLARE_STATIC_KEY_FALSE(tag_storage_enabled_key);
+extern bool page_tag_storage_reserved(struct page *page);
+#endif

static inline void set_page_mte_tagged(struct page *page)
{
+#ifdef CONFIG_ARM64_MTE_TAG_STORAGE
+ /* Open code mte_tag_storage_enabled() */
+ WARN_ON_ONCE(static_branch_likely(&tag_storage_enabled_key) &&
+ !page_tag_storage_reserved(page));
+#endif
/*
* Ensure that the tags written prior to this function are visible
* before the page flags update.
diff --git a/arch/arm64/include/asm/mte_tag_storage.h b/arch/arm64/include/asm/mte_tag_storage.h
index 8f86c4f9a7c3..cab033b184ab 100644
--- a/arch/arm64/include/asm/mte_tag_storage.h
+++ b/arch/arm64/include/asm/mte_tag_storage.h
@@ -5,11 +5,56 @@
#ifndef __ASM_MTE_TAG_STORAGE_H
#define __ASM_MTE_TAG_STORAGE_H

+#ifndef __ASSEMBLY__
+
+#include <linux/mm_types.h>
+
+#include <asm/mte.h>
+
#ifdef CONFIG_ARM64_MTE_TAG_STORAGE
+
+DECLARE_STATIC_KEY_FALSE(tag_storage_enabled_key);
+
+static inline bool tag_storage_enabled(void)
+{
+ return static_branch_likely(&tag_storage_enabled_key);
+}
+
+static inline bool alloc_requires_tag_storage(gfp_t gfp)
+{
+ return gfp & __GFP_TAGGED;
+}
+
void mte_tag_storage_init(void);
+
+int reserve_tag_storage(struct page *page, int order, gfp_t gfp);
+void free_tag_storage(struct page *page, int order);
+
+bool page_tag_storage_reserved(struct page *page);
#else
+static inline bool tag_storage_enabled(void)
+{
+ return false;
+}
+static inline bool alloc_requires_tag_storage(struct page *page)
+{
+ return false;
+}
static inline void mte_tag_storage_init(void)
{
}
+static inline int reserve_tag_storage(struct page *page, int order, gfp_t gfp)
+{
+ return 0;
+}
+static inline void free_tag_storage(struct page *page, int order)
+{
+}
+static inline bool page_tag_storage_reserved(struct page *page)
+{
+ return true;
+}
#endif /* CONFIG_ARM64_MTE_TAG_STORAGE */
+
+#endif /* !__ASSEMBLY__ */
#endif /* __ASM_MTE_TAG_STORAGE_H */
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index cd5dacd1be3a..20e8de853f5d 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -10,6 +10,7 @@

#include <asm/memory.h>
#include <asm/mte.h>
+#include <asm/mte_tag_storage.h>
#include <asm/pgtable-hwdef.h>
#include <asm/pgtable-prot.h>
#include <asm/tlbflush.h>
@@ -1063,6 +1064,32 @@ static inline void arch_swap_restore(swp_entry_t entry, struct folio *folio)
mte_restore_page_tags_by_swp_entry(entry, &folio->page);
}

+#ifdef CONFIG_ARM64_MTE_TAG_STORAGE
+
+#define __HAVE_ARCH_PREP_NEW_PAGE
+static inline int arch_prep_new_page(struct page *page, int order, gfp_t gfp)
+{
+ if (tag_storage_enabled() && alloc_requires_tag_storage(gfp))
+ return reserve_tag_storage(page, order, gfp);
+ return 0;
+}
+
+#define __HAVE_ARCH_FREE_PAGES_PREPARE
+static inline void arch_free_pages_prepare(struct page *page, int order)
+{
+ if (tag_storage_enabled() && page_mte_tagged(page))
+ free_tag_storage(page, order);
+}
+
+#define __HAVE_ARCH_ALLOC_CMA
+static inline bool arch_alloc_cma(gfp_t gfp_mask)
+{
+ if (tag_storage_enabled() && alloc_requires_tag_storage(gfp_mask))
+ return false;
+ return true;
+}
+
+#endif /* CONFIG_ARM64_MTE_TAG_STORAGE */
#endif /* CONFIG_ARM64_MTE */

#define __HAVE_ARCH_CALC_VMA_GFP
diff --git a/arch/arm64/kernel/mte_tag_storage.c b/arch/arm64/kernel/mte_tag_storage.c
index fd63430d4dc0..9f8ef3116fc3 100644
--- a/arch/arm64/kernel/mte_tag_storage.c
+++ b/arch/arm64/kernel/mte_tag_storage.c
@@ -11,12 +11,18 @@
#include <linux/of_device.h>
#include <linux/of_fdt.h>
#include <linux/pageblock-flags.h>
+#include <linux/page-flags.h>
+#include <linux/page_owner.h>
#include <linux/range.h>
+#include <linux/sched/mm.h>
#include <linux/string.h>
+#include <linux/vm_event_item.h>
#include <linux/xarray.h>

#include <asm/mte_tag_storage.h>

+__ro_after_init DEFINE_STATIC_KEY_FALSE(tag_storage_enabled_key);
+
struct tag_region {
struct range mem_range; /* Memory associated with the tag storage, in PFNs. */
struct range tag_range; /* Tag storage memory, in PFNs. */
@@ -28,6 +34,31 @@ struct tag_region {
static struct tag_region tag_regions[MAX_TAG_REGIONS];
static int num_tag_regions;

+/*
+ * A note on locking. Reserving tag storage takes the tag_blocks_lock mutex,
+ * because alloc_contig_range() might sleep.
+ *
+ * Freeing tag storage takes the xa_lock spinlock with interrupts disabled
+ * because pages can be freed from non-preemptible contexts, including from an
+ * interrupt handler.
+ *
+ * Because tag storage can be freed from interrupt contexts, the xarray is
+ * defined with the XA_FLAGS_LOCK_IRQ flag to disable interrupts when calling
+ * xa_store(). This is done to prevent a deadlock with free_tag_storage() being
+ * called from an interrupt raised before xa_store() releases the xa_lock.
+ *
+ * All of the above means that reserve_tag_storage() cannot run concurrently
+ * with itself (no concurrent insertions), but it can run at the same time as
+ * free_tag_storage(). The first thing that reserve_tag_storage() does after
+ * taking the mutex is increase the refcount on all present tag storage blocks
+ * with the xa_lock held, to serialize against freeing the blocks. This is an
+ * optimization to avoid taking and releasing the xa_lock after each iteration
+ * if the refcount operation was moved inside the loop, where it would have had
+ * to be executed for each block.
+ */
+static DEFINE_XARRAY_FLAGS(tag_blocks_reserved, XA_FLAGS_LOCK_IRQ);
+static DEFINE_MUTEX(tag_blocks_lock);
+
static int __init tag_storage_of_flat_get_range(unsigned long node, const __be32 *reg,
int reg_len, struct range *range)
{
@@ -368,3 +399,213 @@ static int __init mte_tag_storage_activate_regions(void)
return ret;
}
arch_initcall(mte_tag_storage_activate_regions);
+
+static void page_set_tag_storage_reserved(struct page *page, int order)
+{
+ int i;
+
+ for (i = 0; i < (1 << order); i++)
+ set_bit(PG_tag_storage_reserved, &(page + i)->flags);
+}
+
+static void block_ref_add(unsigned long block, struct tag_region *region, int order)
+{
+ int count;
+
+ count = min(1u << order, 32 * region->block_size);
+ page_ref_add(pfn_to_page(block), count);
+}
+
+static int block_ref_sub_return(unsigned long block, struct tag_region *region, int order)
+{
+ int count;
+
+ count = min(1u << order, 32 * region->block_size);
+ return page_ref_sub_return(pfn_to_page(block), count);
+}
+
+static bool tag_storage_block_is_reserved(unsigned long block)
+{
+ return xa_load(&tag_blocks_reserved, block) != NULL;
+}
+
+static int tag_storage_reserve_block(unsigned long block, struct tag_region *region, int order)
+{
+ int ret;
+
+ ret = xa_err(xa_store(&tag_blocks_reserved, block, pfn_to_page(block), GFP_KERNEL));
+ if (!ret)
+ block_ref_add(block, region, order);
+
+ return ret;
+}
+
+static int order_to_num_blocks(int order)
+{
+ return max((1 << order) / 32, 1);
+}
+
+static int tag_storage_find_block_in_region(struct page *page, unsigned long *blockp,
+ struct tag_region *region)
+{
+ struct range *tag_range = &region->tag_range;
+ struct range *mem_range = &region->mem_range;
+ u64 page_pfn = page_to_pfn(page);
+ u64 block, block_offset;
+
+ if (!(mem_range->start <= page_pfn && page_pfn <= mem_range->end))
+ return -ERANGE;
+
+ block_offset = (page_pfn - mem_range->start) / 32;
+ block = tag_range->start + rounddown(block_offset, region->block_size);
+
+ if (block + region->block_size - 1 > tag_range->end) {
+ pr_err("Block 0x%llx-0x%llx is outside tag region 0x%llx-0x%llx\n",
+ PFN_PHYS(block), PFN_PHYS(block + region->block_size),
+ PFN_PHYS(tag_range->start), PFN_PHYS(tag_range->end));
+ return -ERANGE;
+ }
+ *blockp = block;
+
+ return 0;
+
+}
+
+static int tag_storage_find_block(struct page *page, unsigned long *block,
+ struct tag_region **region)
+{
+ int i, ret;
+
+ for (i = 0; i < num_tag_regions; i++) {
+ ret = tag_storage_find_block_in_region(page, block, &tag_regions[i]);
+ if (ret == 0) {
+ *region = &tag_regions[i];
+ return 0;
+ }
+ }
+
+ return -EINVAL;
+}
+
+bool page_tag_storage_reserved(struct page *page)
+{
+ return test_bit(PG_tag_storage_reserved, &page->flags);
+}
+
+int reserve_tag_storage(struct page *page, int order, gfp_t gfp)
+{
+ unsigned long start_block, end_block;
+ struct tag_region *region;
+ unsigned long block;
+ unsigned long flags;
+ unsigned int tries;
+ int ret = 0;
+
+ VM_WARN_ON_ONCE(!preemptible());
+
+ if (page_tag_storage_reserved(page))
+ return 0;
+
+ /*
+ * __alloc_contig_migrate_range() ignores gfp when allocating the
+ * destination page for migration. Regardless, massage gfp flags and
+ * remove __GFP_TAGGED to avoid recursion in case gfp stops being
+ * ignored.
+ */
+ gfp &= ~__GFP_TAGGED;
+ if (!(gfp & __GFP_NORETRY))
+ gfp |= __GFP_RETRY_MAYFAIL;
+
+ ret = tag_storage_find_block(page, &start_block, &region);
+ if (WARN_ONCE(ret, "Missing tag storage block for pfn 0x%lx", page_to_pfn(page)))
+ return 0;
+ end_block = start_block + order_to_num_blocks(order) * region->block_size;
+
+ mutex_lock(&tag_blocks_lock);
+
+ /* Check again, this time with the lock held. */
+ if (page_tag_storage_reserved(page))
+ goto out_unlock;
+
+ /* Make sure existing entries are not freed from out under out feet. */
+ xa_lock_irqsave(&tag_blocks_reserved, flags);
+ for (block = start_block; block < end_block; block += region->block_size) {
+ if (tag_storage_block_is_reserved(block))
+ block_ref_add(block, region, order);
+ }
+ xa_unlock_irqrestore(&tag_blocks_reserved, flags);
+
+ for (block = start_block; block < end_block; block += region->block_size) {
+ /* Refcount incremented above. */
+ if (tag_storage_block_is_reserved(block))
+ continue;
+
+ tries = 3;
+ while (tries--) {
+ ret = alloc_contig_range(block, block + region->block_size, MIGRATE_CMA, gfp);
+ if (ret == 0 || ret != -EBUSY)
+ break;
+ }
+
+ if (ret)
+ goto out_error;
+
+ ret = tag_storage_reserve_block(block, region, order);
+ if (ret) {
+ free_contig_range(block, region->block_size);
+ goto out_error;
+ }
+
+ count_vm_events(CMA_ALLOC_SUCCESS, region->block_size);
+ }
+
+ page_set_tag_storage_reserved(page, order);
+out_unlock:
+ mutex_unlock(&tag_blocks_lock);
+
+ return 0;
+
+out_error:
+ xa_lock_irqsave(&tag_blocks_reserved, flags);
+ for (block = start_block; block < end_block; block += region->block_size) {
+ if (tag_storage_block_is_reserved(block) &&
+ block_ref_sub_return(block, region, order) == 1) {
+ __xa_erase(&tag_blocks_reserved, block);
+ free_contig_range(block, region->block_size);
+ }
+ }
+ xa_unlock_irqrestore(&tag_blocks_reserved, flags);
+
+ mutex_unlock(&tag_blocks_lock);
+
+ count_vm_events(CMA_ALLOC_FAIL, region->block_size);
+
+ return ret;
+}
+
+void free_tag_storage(struct page *page, int order)
+{
+ unsigned long block, start_block, end_block;
+ struct tag_region *region;
+ unsigned long flags;
+ int ret;
+
+ ret = tag_storage_find_block(page, &start_block, &region);
+ if (WARN_ONCE(ret, "Missing tag storage block for pfn 0x%lx", page_to_pfn(page)))
+ return;
+
+ end_block = start_block + order_to_num_blocks(order) * region->block_size;
+
+ xa_lock_irqsave(&tag_blocks_reserved, flags);
+ for (block = start_block; block < end_block; block += region->block_size) {
+ if (WARN_ONCE(!tag_storage_block_is_reserved(block),
+ "Block 0x%lx is not reserved for pfn 0x%lx", block, page_to_pfn(page)))
+ continue;
+
+ if (block_ref_sub_return(block, region, order) == 1) {
+ __xa_erase(&tag_blocks_reserved, block);
+ free_contig_range(block, region->block_size);
+ }
+ }
+ xa_unlock_irqrestore(&tag_blocks_reserved, flags);
+}
diff --git a/fs/proc/page.c b/fs/proc/page.c
index 195b077c0fac..e7eb584a9234 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -221,6 +221,7 @@ u64 stable_page_flags(struct page *page)
#ifdef CONFIG_ARCH_USES_PG_ARCH_X
u |= kpf_copy_bit(k, KPF_ARCH_2, PG_arch_2);
u |= kpf_copy_bit(k, KPF_ARCH_3, PG_arch_3);
+ u |= kpf_copy_bit(k, KPF_ARCH_4, PG_arch_4);
#endif

return u;
diff --git a/include/linux/kernel-page-flags.h b/include/linux/kernel-page-flags.h
index 859f4b0c1b2b..4a0d719ffdd4 100644
--- a/include/linux/kernel-page-flags.h
+++ b/include/linux/kernel-page-flags.h
@@ -19,5 +19,6 @@
#define KPF_SOFTDIRTY 40
#define KPF_ARCH_2 41
#define KPF_ARCH_3 42
+#define KPF_ARCH_4 43

#endif /* LINUX_KERNEL_PAGE_FLAGS_H */
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index a88e64acebfe..7915165a51bd 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -135,6 +135,7 @@ enum pageflags {
#ifdef CONFIG_ARCH_USES_PG_ARCH_X
PG_arch_2,
PG_arch_3,
+ PG_arch_4,
#endif
__NR_PAGEFLAGS,

diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index 6ca0d5ed46c0..ba962fd10a2c 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -125,7 +125,8 @@ IF_HAVE_PG_HWPOISON(hwpoison) \
IF_HAVE_PG_IDLE(idle) \
IF_HAVE_PG_IDLE(young) \
IF_HAVE_PG_ARCH_X(arch_2) \
-IF_HAVE_PG_ARCH_X(arch_3)
+IF_HAVE_PG_ARCH_X(arch_3) \
+IF_HAVE_PG_ARCH_X(arch_4)

#define show_page_flags(flags) \
(flags) ? __print_flags(flags, "|", \
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f31f02472396..9beead961a65 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2474,6 +2474,7 @@ static void __split_huge_page_tail(struct folio *folio, int tail,
#ifdef CONFIG_ARCH_USES_PG_ARCH_X
(1L << PG_arch_2) |
(1L << PG_arch_3) |
+ (1L << PG_arch_4) |
#endif
(1L << PG_dirty) |
LRU_GEN_MASK | LRU_REFS_MASK));
--
2.42.1