[PATCH v3 6/6] mm: secretmem: add ability to reserve memory at boot

[Mike Rapoport]

From: Mike Rapoport <rppt@xxxxxxxxxxxxx>

Taking pages out from the direct map and bringing them back may create
undesired fragmentation and usage of the smaller pages in the direct
mapping of the physical memory.

This can be avoided if a significantly large area of the physical memory
would be reserved for secretmem purposes at boot time.

Add ability to reserve physical memory for secretmem at boot time using
"secretmem" kernel parameter and then use that reserved memory as a global
pool for secret memory needs.

Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
---
 mm/secretmem.c | 134 ++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 126 insertions(+), 8 deletions(-)

diff --git a/mm/secretmem.c b/mm/secretmem.c
index e42616785a88..0f3e7b30a0a7 100644
--- a/mm/secretmem.c
+++ b/mm/secretmem.c
@@ -8,6 +8,7 @@
 #include <linux/pagemap.h>
 #include <linux/genalloc.h>
 #include <linux/syscalls.h>
+#include <linux/memblock.h>
 #include <linux/pseudo_fs.h>
 #include <linux/set_memory.h>
 #include <linux/sched/signal.h>
@@ -35,6 +36,39 @@ struct secretmem_ctx {
 	unsigned int mode;
 };
 
+struct secretmem_pool {
+	struct gen_pool *pool;
+	unsigned long reserved_size;
+	void *reserved;
+};
+
+static struct secretmem_pool secretmem_pool;
+
+static struct page *secretmem_alloc_huge_page(gfp_t gfp)
+{
+	struct gen_pool *pool = secretmem_pool.pool;
+	unsigned long addr = 0;
+	struct page *page = NULL;
+
+	if (pool) {
+		if (gen_pool_avail(pool) < PMD_SIZE)
+			return NULL;
+
+		addr = gen_pool_alloc(pool, PMD_SIZE);
+		if (!addr)
+			return NULL;
+
+		page = virt_to_page(addr);
+	} else {
+		page = alloc_pages(gfp, PMD_PAGE_ORDER);
+
+		if (page)
+			split_page(page, PMD_PAGE_ORDER);
+	}
+
+	return page;
+}
+
 static int secretmem_pool_increase(struct secretmem_ctx *ctx, gfp_t gfp)
 {
 	unsigned long nr_pages = (1 << PMD_PAGE_ORDER);
@@ -43,12 +77,11 @@ static int secretmem_pool_increase(struct secretmem_ctx *ctx, gfp_t gfp)
 	struct page *page;
 	int err;
 
-	page = alloc_pages(gfp, PMD_PAGE_ORDER);
+	page = secretmem_alloc_huge_page(gfp);
 	if (!page)
 		return -ENOMEM;
 
 	addr = (unsigned long)page_address(page);
-	split_page(page, PMD_PAGE_ORDER);
 
 	err = gen_pool_add(pool, addr, PMD_SIZE, NUMA_NO_NODE);
 	if (err) {
@@ -274,11 +307,13 @@ SYSCALL_DEFINE1(memfd_secret, unsigned long, flags)
 	return err;
 }
 
-static void secretmem_cleanup_chunk(struct gen_pool *pool,
-				    struct gen_pool_chunk *chunk, void *data)
+static void secretmem_recycle_range(unsigned long start, unsigned long end)
+{
+	gen_pool_free(secretmem_pool.pool, start, PMD_SIZE);
+}
+
+static void secretmem_release_range(unsigned long start, unsigned long end)
 {
-	unsigned long start = chunk->start_addr;
-	unsigned long end = chunk->end_addr;
 	unsigned long nr_pages, addr;
 
 	nr_pages = (end - start + 1) / PAGE_SIZE;
@@ -288,6 +323,18 @@ static void secretmem_cleanup_chunk(struct gen_pool *pool,
 		put_page(virt_to_page(addr));
 }
 
+static void secretmem_cleanup_chunk(struct gen_pool *pool,
+				    struct gen_pool_chunk *chunk, void *data)
+{
+	unsigned long start = chunk->start_addr;
+	unsigned long end = chunk->end_addr;
+
+	if (secretmem_pool.pool)
+		secretmem_recycle_range(start, end);
+	else
+		secretmem_release_range(start, end);
+}
+
 static void secretmem_cleanup_pool(struct secretmem_ctx *ctx)
 {
 	struct gen_pool *pool = ctx->pool;
@@ -327,14 +374,85 @@ static struct file_system_type secretmem_fs = {
 	.kill_sb	= kill_anon_super,
 };
 
+static int secretmem_reserved_mem_init(void)
+{
+	struct gen_pool *pool;
+	struct page *page;
+	void *addr;
+	int err;
+
+	if (!secretmem_pool.reserved)
+		return 0;
+
+	pool = gen_pool_create(PMD_SHIFT, NUMA_NO_NODE);
+	if (!pool)
+		return -ENOMEM;
+
+	err = gen_pool_add(pool, (unsigned long)secretmem_pool.reserved,
+			   secretmem_pool.reserved_size, NUMA_NO_NODE);
+	if (err)
+		goto err_destroy_pool;
+
+	for (addr = secretmem_pool.reserved;
+	     addr < secretmem_pool.reserved + secretmem_pool.reserved_size;
+	     addr += PAGE_SIZE) {
+		page = virt_to_page(addr);
+		__ClearPageReserved(page);
+		set_page_count(page, 1);
+	}
+
+	secretmem_pool.pool = pool;
+	page = virt_to_page(secretmem_pool.reserved);
+	__kernel_map_pages(page, secretmem_pool.reserved_size / PAGE_SIZE, 0);
+	return 0;
+
+err_destroy_pool:
+	gen_pool_destroy(pool);
+	return err;
+}
+
 static int secretmem_init(void)
 {
-	int ret = 0;
+	int ret;
+
+	ret = secretmem_reserved_mem_init();
+	if (ret)
+		return ret;
 
 	secretmem_mnt = kern_mount(&secretmem_fs);
-	if (IS_ERR(secretmem_mnt))
+	if (IS_ERR(secretmem_mnt)) {
+		gen_pool_destroy(secretmem_pool.pool);
 		ret = PTR_ERR(secretmem_mnt);
+	}
 
 	return ret;
 }
 fs_initcall(secretmem_init);
+
+static int __init secretmem_setup(char *str)
+{
+	phys_addr_t align = PMD_SIZE;
+	unsigned long reserved_size;
+	void *reserved;
+
+	reserved_size = memparse(str, NULL);
+	if (!reserved_size)
+		return 0;
+
+	if (reserved_size * 2 > PUD_SIZE)
+		align = PUD_SIZE;
+
+	reserved = memblock_alloc(reserved_size, align);
+	if (!reserved) {
+		pr_err("failed to reserve %lu bytes\n", secretmem_pool.reserved_size);
+		return 0;
+	}
+
+	secretmem_pool.reserved_size = reserved_size;
+	secretmem_pool.reserved = reserved;
+
+	pr_info("reserved %luM\n", reserved_size >> 20);
+
+	return 1;
+}
+__setup("secretmem=", secretmem_setup);
-- 
2.26.2