[PATCH v15 07/11] secretmem: use PMD-size pages to amortize direct map fragmentation
Mike Rapoport
rppt at kernel.org
Wed Jan 20 13:06:08 EST 2021
From: Mike Rapoport <rppt at linux.ibm.com>
Removing a PAGE_SIZE page from the direct map every time such page is
allocated for a secret memory mapping will cause severe fragmentation of
the direct map. This fragmentation can be reduced by using PMD-size pages
as a pool for small pages for secret memory mappings.
Add a gen_pool per secretmem inode and lazily populate this pool with
PMD-size pages.
As pages allocated by secretmem become unmovable, use CMA to back large
page caches so that page allocator won't be surprised by failing attempt to
migrate these pages.
The CMA area used by secretmem is controlled by the "secretmem=" kernel
parameter. This allows explicit control over the memory available for
secretmem and provides upper hard limit for secretmem consumption.
Signed-off-by: Mike Rapoport <rppt at linux.ibm.com>
Cc: Alexander Viro <viro at zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto at kernel.org>
Cc: Arnd Bergmann <arnd at arndb.de>
Cc: Borislav Petkov <bp at alien8.de>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Christopher Lameter <cl at linux.com>
Cc: Dan Williams <dan.j.williams at intel.com>
Cc: Dave Hansen <dave.hansen at linux.intel.com>
Cc: David Hildenbrand <david at redhat.com>
Cc: Elena Reshetova <elena.reshetova at intel.com>
Cc: Hagen Paul Pfeifer <hagen at jauu.net>
Cc: "H. Peter Anvin" <hpa at zytor.com>
Cc: Ingo Molnar <mingo at redhat.com>
Cc: James Bottomley <jejb at linux.ibm.com>
Cc: "Kirill A. Shutemov" <kirill at shutemov.name>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Matthew Wilcox <willy at infradead.org>
Cc: Michael Kerrisk <mtk.manpages at gmail.com>
Cc: Palmer Dabbelt <palmer at dabbelt.com>
Cc: Palmer Dabbelt <palmerdabbelt at google.com>
Cc: Paul Walmsley <paul.walmsley at sifive.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Rick Edgecombe <rick.p.edgecombe at intel.com>
Cc: Roman Gushchin <guro at fb.com>
Cc: Shakeel Butt <shakeelb at google.com>
Cc: Shuah Khan <shuah at kernel.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Tycho Andersen <tycho at tycho.ws>
Cc: Will Deacon <will at kernel.org>
---
mm/Kconfig | 2 +
mm/secretmem.c | 166 +++++++++++++++++++++++++++++++++++++++++--------
2 files changed, 143 insertions(+), 25 deletions(-)
diff --git a/mm/Kconfig b/mm/Kconfig
index 5f8243442f66..ec35bf406439 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -874,5 +874,7 @@ config KMAP_LOCAL
config SECRETMEM
def_bool ARCH_HAS_SET_DIRECT_MAP && !EMBEDDED
+ select GENERIC_ALLOCATOR
+ select CMA
endmenu
diff --git a/mm/secretmem.c b/mm/secretmem.c
index 2b4c20113412..fe193bdedd76 100644
--- a/mm/secretmem.c
+++ b/mm/secretmem.c
@@ -7,12 +7,15 @@
#include <linux/mm.h>
#include <linux/fs.h>
+#include <linux/cma.h>
#include <linux/mount.h>
#include <linux/memfd.h>
#include <linux/bitops.h>
#include <linux/printk.h>
#include <linux/pagemap.h>
+#include <linux/genalloc.h>
#include <linux/syscalls.h>
+#include <linux/memblock.h>
#include <linux/pseudo_fs.h>
#include <linux/secretmem.h>
#include <linux/set_memory.h>
@@ -35,24 +38,87 @@
#define SECRETMEM_FLAGS_MASK SECRETMEM_MODE_MASK
struct secretmem_ctx {
+ struct gen_pool *pool;
unsigned int mode;
};
-static struct page *secretmem_alloc_page(gfp_t gfp)
+static struct cma *secretmem_cma;
+
+static int secretmem_pool_increase(struct secretmem_ctx *ctx, gfp_t gfp)
{
+ unsigned long nr_pages = (1 << PMD_PAGE_ORDER);
+ struct gen_pool *pool = ctx->pool;
+ unsigned long addr;
+ struct page *page;
+ int err;
+
+ page = cma_alloc(secretmem_cma, nr_pages, PMD_SIZE, gfp & __GFP_NOWARN);
+ if (!page)
+ return -ENOMEM;
+
+ err = set_direct_map_invalid_noflush(page, nr_pages);
+ if (err)
+ goto err_cma_release;
+
+ addr = (unsigned long)page_address(page);
+ err = gen_pool_add(pool, addr, PMD_SIZE, NUMA_NO_NODE);
+ if (err)
+ goto err_set_direct_map;
+
+ flush_tlb_kernel_range(addr, addr + PMD_SIZE);
+
+ return 0;
+
+err_set_direct_map:
/*
- * FIXME: use a cache of large pages to reduce the direct map
- * fragmentation
+ * If a split of PUD-size page was required, it already happened
+ * when we marked the pages invalid which guarantees that this call
+ * won't fail
*/
- return alloc_page(gfp);
+ set_direct_map_default_noflush(page, nr_pages);
+err_cma_release:
+ cma_release(secretmem_cma, page, nr_pages);
+ return err;
+}
+
+static void secretmem_free_page(struct secretmem_ctx *ctx, struct page *page)
+{
+ unsigned long addr = (unsigned long)page_address(page);
+ struct gen_pool *pool = ctx->pool;
+
+ gen_pool_free(pool, addr, PAGE_SIZE);
+}
+
+static struct page *secretmem_alloc_page(struct secretmem_ctx *ctx,
+ gfp_t gfp)
+{
+ struct gen_pool *pool = ctx->pool;
+ unsigned long addr;
+ struct page *page;
+ int err;
+
+ if (gen_pool_avail(pool) < PAGE_SIZE) {
+ err = secretmem_pool_increase(ctx, gfp);
+ if (err)
+ return NULL;
+ }
+
+ addr = gen_pool_alloc(pool, PAGE_SIZE);
+ if (!addr)
+ return NULL;
+
+ page = virt_to_page(addr);
+ get_page(page);
+
+ return page;
}
static vm_fault_t secretmem_fault(struct vm_fault *vmf)
{
+ struct secretmem_ctx *ctx = vmf->vma->vm_file->private_data;
struct address_space *mapping = vmf->vma->vm_file->f_mapping;
struct inode *inode = file_inode(vmf->vma->vm_file);
pgoff_t offset = vmf->pgoff;
- unsigned long addr;
struct page *page;
int err;
@@ -62,38 +128,25 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf)
retry:
page = find_lock_page(mapping, offset);
if (!page) {
- page = secretmem_alloc_page(vmf->gfp_mask);
+ page = secretmem_alloc_page(ctx, vmf->gfp_mask);
if (!page)
return VM_FAULT_OOM;
- err = set_direct_map_invalid_noflush(page, 1);
- if (err)
- return vmf_error(err);
-
__SetPageUptodate(page);
err = add_to_page_cache(page, mapping, offset, vmf->gfp_mask);
if (unlikely(err)) {
+ secretmem_free_page(ctx, page);
put_page(page);
if (err == -EEXIST)
goto retry;
- goto err_restore_direct_map;
+ return vmf_error(err);
}
- addr = (unsigned long)page_address(page);
- flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
+ set_page_private(page, (unsigned long)ctx);
}
vmf->page = page;
return VM_FAULT_LOCKED;
-
-err_restore_direct_map:
- /*
- * If a split of large page was required, it already happened
- * when we marked the page invalid which guarantees that this call
- * won't fail
- */
- set_direct_map_default_noflush(page, 1);
- return vmf_error(err);
}
static const struct vm_operations_struct secretmem_vm_ops = {
@@ -139,8 +192,9 @@ static int secretmem_migratepage(struct address_space *mapping,
static void secretmem_freepage(struct page *page)
{
- set_direct_map_default_noflush(page, 1);
- clear_highpage(page);
+ struct secretmem_ctx *ctx = (struct secretmem_ctx *)page_private(page);
+
+ secretmem_free_page(ctx, page);
}
static const struct address_space_operations secretmem_aops = {
@@ -175,13 +229,18 @@ static struct file *secretmem_file_create(unsigned long flags)
if (!ctx)
goto err_free_inode;
+ ctx->pool = gen_pool_create(PAGE_SHIFT, NUMA_NO_NODE);
+ if (!ctx->pool)
+ goto err_free_ctx;
+
file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
O_RDWR, &secretmem_fops);
if (IS_ERR(file))
- goto err_free_ctx;
+ goto err_free_pool;
mapping_set_unevictable(inode->i_mapping);
+ inode->i_private = ctx;
inode->i_mapping->private_data = ctx;
inode->i_mapping->a_ops = &secretmem_aops;
@@ -195,6 +254,8 @@ static struct file *secretmem_file_create(unsigned long flags)
return file;
+err_free_pool:
+ gen_pool_destroy(ctx->pool);
err_free_ctx:
kfree(ctx);
err_free_inode:
@@ -213,6 +274,9 @@ SYSCALL_DEFINE1(memfd_secret, unsigned long, flags)
if (flags & ~(SECRETMEM_FLAGS_MASK | O_CLOEXEC))
return -EINVAL;
+ if (!secretmem_cma)
+ return -ENOMEM;
+
fd = get_unused_fd_flags(flags & O_CLOEXEC);
if (fd < 0)
return fd;
@@ -233,11 +297,37 @@ 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)
+{
+ unsigned long start = chunk->start_addr;
+ unsigned long end = chunk->end_addr;
+ struct page *page = virt_to_page(start);
+ unsigned long nr_pages = (end - start + 1) / PAGE_SIZE;
+ int i;
+
+ set_direct_map_default_noflush(page, nr_pages);
+
+ for (i = 0; i < nr_pages; i++)
+ clear_highpage(page + i);
+
+ cma_release(secretmem_cma, page, nr_pages);
+}
+
+static void secretmem_cleanup_pool(struct secretmem_ctx *ctx)
+{
+ struct gen_pool *pool = ctx->pool;
+
+ gen_pool_for_each_chunk(pool, secretmem_cleanup_chunk, ctx);
+ gen_pool_destroy(pool);
+}
+
static void secretmem_evict_inode(struct inode *inode)
{
struct secretmem_ctx *ctx = inode->i_private;
truncate_inode_pages_final(&inode->i_data);
+ secretmem_cleanup_pool(ctx);
clear_inode(inode);
kfree(ctx);
}
@@ -274,3 +364,29 @@ static int secretmem_init(void)
return ret;
}
fs_initcall(secretmem_init);
+
+static int __init secretmem_setup(char *str)
+{
+ phys_addr_t align = PMD_SIZE;
+ unsigned long reserved_size;
+ int err;
+
+ reserved_size = memparse(str, NULL);
+ if (!reserved_size)
+ return 0;
+
+ if (reserved_size * 2 > PUD_SIZE)
+ align = PUD_SIZE;
+
+ err = cma_declare_contiguous(0, reserved_size, 0, align, 0, false,
+ "secretmem", &secretmem_cma);
+ if (err) {
+ pr_err("failed to create CMA: %d\n", err);
+ return err;
+ }
+
+ pr_info("reserved %luM\n", reserved_size >> 20);
+
+ return 0;
+}
+__setup("secretmem=", secretmem_setup);
--
2.28.0
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