[PATCH RFC v3 23/35] arm64: mte: Try to reserve tag storage in arch_alloc_page()

From: Alexandru Elisei
Date: Thu Jan 25 2024 - 11:53:23 EST

Reserve tag storage for a page that is being allocated as tagged. This
is a best effort approach, and failing to reserve tag storage is
allowed.

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.

Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
---

Changes since rfc v2:

* Based on rfc v2 patch #16 ("arm64: mte: Manage tag storage on page
allocation").
* Fixed calculation of the number of associated tag storage blocks (Hyesoo
Yu).
* Tag storage is reserved in arch_alloc_page() instead of
arch_prep_new_page().

arch/arm64/include/asm/mte.h | 16 +-
arch/arm64/include/asm/mte_tag_storage.h | 31 +++
arch/arm64/include/asm/page.h | 5 +
arch/arm64/include/asm/pgtable.h | 19 ++
arch/arm64/kernel/mte_tag_storage.c | 234 +++++++++++++++++++++++
arch/arm64/mm/fault.c | 7 +
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 +
11 files changed, 316 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 7b3f6bff8e6f..09f1318d924e 100644
--- a/arch/arm64/include/asm/mte_tag_storage.h
+++ b/arch/arm64/include/asm/mte_tag_storage.h
@@ -5,6 +5,12 @@
#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);
@@ -15,6 +21,15 @@ static inline bool tag_storage_enabled(void)
}

void mte_init_tag_storage(void);
+
+static inline bool alloc_requires_tag_storage(gfp_t gfp)
+{
+ return gfp & __GFP_TAGGED;
+}
+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)
{
@@ -23,6 +38,22 @@ static inline bool tag_storage_enabled(void)
static inline void mte_init_tag_storage(void)
{
}
+static inline bool alloc_requires_tag_storage(struct page *page)
+{
+ return false;
+}
+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/page.h b/arch/arm64/include/asm/page.h
index 88bab032a493..3a656492f34a 100644
--- a/arch/arm64/include/asm/page.h
+++ b/arch/arm64/include/asm/page.h
@@ -35,6 +35,11 @@ void copy_highpage(struct page *to, struct page *from);
void tag_clear_highpage(struct page *to);
#define __HAVE_ARCH_TAG_CLEAR_HIGHPAGE

+#ifdef CONFIG_ARM64_MTE_TAG_STORAGE
+void arch_alloc_page(struct page *, int order, gfp_t gfp);
+#define HAVE_ARCH_ALLOC_PAGE
+#endif
+
#define clear_user_page(page, vaddr, pg) clear_page(page)
#define copy_user_page(to, from, vaddr, pg) copy_page(to, from)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 2499cc4fa4f2..f30466199a9b 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>
@@ -1069,6 +1070,24 @@ 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_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 d58c68b4a849..762c7c803a70 100644
--- a/arch/arm64/kernel/mte_tag_storage.c
+++ b/arch/arm64/kernel/mte_tag_storage.c
@@ -34,6 +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 u32 __init get_block_size_pages(u32 block_size_bytes)
{
u32 a = PAGE_SIZE;
@@ -364,3 +389,212 @@ static int __init mte_enable_tag_storage(void)
return -EINVAL;
}
arch_initcall(mte_enable_tag_storage);
+
+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_pages);
+ 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_pages);
+ 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, u32 block_size_pages)
+{
+ int num_tag_storage_pages = max((1 << order) / 32, 1);
+
+ return DIV_ROUND_UP(num_tag_storage_pages, block_size_pages);
+}
+
+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_pages);
+
+ if (block + region->block_size_pages - 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_pages + 1) - 1,
+ PFN_PHYS(tag_range->start), PFN_PHYS(tag_range->end + 1) - 1);
+ 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;
+ 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 -EINVAL;
+ end_block = start_block + order_to_num_blocks(order, region->block_size_pages);
+
+ 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_pages) {
+ 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_pages) {
+ /* Refcount incremented above. */
+ if (tag_storage_block_is_reserved(block))
+ continue;
+
+ ret = cma_alloc_range(region->cma, block, region->block_size_pages, 3, gfp);
+ /* Should never happen. */
+ VM_WARN_ON_ONCE(ret == -EEXIST);
+ if (ret)
+ goto out_error;
+
+ ret = tag_storage_reserve_block(block, region, order);
+ if (ret) {
+ cma_release(region->cma, pfn_to_page(block), region->block_size_pages);
+ goto out_error;
+ }
+ }
+
+ 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_pages) {
+ if (tag_storage_block_is_reserved(block) &&
+ block_ref_sub_return(block, region, order) == 1) {
+ __xa_erase(&tag_blocks_reserved, block);
+ cma_release(region->cma, pfn_to_page(block), region->block_size_pages);
+ }
+ }
+ xa_unlock_irqrestore(&tag_blocks_reserved, flags);
+
+ mutex_unlock(&tag_blocks_lock);
+
+ 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_pages);
+
+ xa_lock_irqsave(&tag_blocks_reserved, flags);
+ for (block = start_block; block < end_block; block += region->block_size_pages) {
+ 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);
+ cma_release(region->cma, pfn_to_page(block), region->block_size_pages);
+ }
+ }
+ xa_unlock_irqrestore(&tag_blocks_reserved, flags);
+}
+
+void arch_alloc_page(struct page *page, int order, gfp_t gfp)
+{
+ if (tag_storage_enabled() && alloc_requires_tag_storage(gfp))
+ reserve_tag_storage(page, order, gfp);
+}
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index c022e473c17c..1ffaeccecda2 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -37,6 +37,7 @@
#include <asm/esr.h>
#include <asm/kprobes.h>
#include <asm/mte.h>
+#include <asm/mte_tag_storage.h>
#include <asm/processor.h>
#include <asm/sysreg.h>
#include <asm/system_misc.h>
@@ -950,6 +951,12 @@ gfp_t arch_calc_vma_gfp(struct vm_area_struct *vma, gfp_t gfp)

void tag_clear_highpage(struct page *page)
{
+ if (tag_storage_enabled() && !page_tag_storage_reserved(page)) {
+ /* Don't zero the tags if tag storage is not reserved */
+ clear_page(page_address(page));
+ return;
+ }
+
/* Newly allocated page, shouldn't have been tagged yet */
WARN_ON_ONCE(!try_page_mte_tagging(page));
mte_zero_clear_page_tags(page_address(page));
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 b7237bce7446..03f03e6d735e 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 2bad63a7ec16..47932539cc50 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2804,6 +2804,7 @@ 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));
--
2.43.0