[PATCH v2 4/4] x86/vmalloc: Add TLB efficient x86 arch_vunmap

Rick Edgecombe
2018-12-12T00:12:11Z

This adds a more efficient x86 architecture specific implementation of
arch_vunmap, that can free any type of special permission memory with only 1 TLB
flush.

In order to enable this, _set_pages_p and _set_pages_np are made non-static and
renamed set_pages_p_noflush and set_pages_np_noflush to better communicate
their different (non-flushing) behavior from the rest of the set_pages_*
functions.

The method for doing this with only 1 TLB flush was suggested by Andy
Lutomirski.

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
arch/x86/include/asm/set_memory.h | 2 +
arch/x86/mm/Makefile | 3 +-
arch/x86/mm/pageattr.c | 11 +++--
arch/x86/mm/vmalloc.c | 71 +++++++++++++++++++++++++++++++
4 files changed, 80 insertions(+), 7 deletions(-)
create mode 100644 arch/x86/mm/vmalloc.c

diff --git a/arch/x86/include/asm/set_memory.h b/arch/x86/include/asm/set_memory.h
index 07a25753e85c..70ee81e8914b 100644
--- a/arch/x86/include/asm/set_memory.h
+++ b/arch/x86/include/asm/set_memory.h
@@ -84,6 +84,8 @@ int set_pages_x(struct page *page, int numpages);
int set_pages_nx(struct page *page, int numpages);
int set_pages_ro(struct page *page, int numpages);
int set_pages_rw(struct page *page, int numpages);
+int set_pages_np_noflush(struct page *page, int numpages);
+int set_pages_p_noflush(struct page *page, int numpages);

extern int kernel_set_to_readonly;
void set_kernel_text_rw(void);
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index 4b101dd6e52f..189681f863a6 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -13,7 +13,8 @@ CFLAGS_REMOVE_mem_encrypt_identity.o = -pg
endif

obj-y := init.o init_$(BITS).o fault.o ioremap.o extable.o pageattr.o mmap.o \
- pat.o pgtable.o physaddr.o setup_nx.o tlb.o cpu_entry_area.o
+ pat.o pgtable.o physaddr.o setup_nx.o tlb.o cpu_entry_area.o \
+ vmalloc.o

# Make sure __phys_addr has no stackprotector
nostackp := $(call cc-option, -fno-stack-protector)
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index db7a10082238..db0a4dfb5a7f 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -2248,9 +2248,7 @@ int set_pages_rw(struct page *page, int numpages)
return set_memory_rw(addr, numpages);
}

-#ifdef CONFIG_DEBUG_PAGEALLOC
-
-static int __set_pages_p(struct page *page, int numpages)
+int set_pages_p_noflush(struct page *page, int numpages)
{
unsigned long tempaddr = (unsigned long) page_address(page);
struct cpa_data cpa = { .vaddr = &tempaddr,
@@ -2269,7 +2267,7 @@ static int __set_pages_p(struct page *page, int numpages)
return __change_page_attr_set_clr(&cpa, 0);
}

-static int __set_pages_np(struct page *page, int numpages)
+int set_pages_np_noflush(struct page *page, int numpages)
{
unsigned long tempaddr = (unsigned long) page_address(page);
struct cpa_data cpa = { .vaddr = &tempaddr,
@@ -2288,6 +2286,7 @@ static int __set_pages_np(struct page *page, int numpages)
return __change_page_attr_set_clr(&cpa, 0);
}

+#ifdef CONFIG_DEBUG_PAGEALLOC
void __kernel_map_pages(struct page *page, int numpages, int enable)
{
if (PageHighMem(page))
@@ -2303,9 +2302,9 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
* and hence no memory allocations during large page split.
*/
if (enable)
- __set_pages_p(page, numpages);
+ set_pages_p_noflush(page, numpages);
else
- __set_pages_np(page, numpages);
+ set_pages_np_noflush(page, numpages);

/*
* We should perform an IPI and flush all tlbs,
diff --git a/arch/x86/mm/vmalloc.c b/arch/x86/mm/vmalloc.c
new file mode 100644
index 000000000000..be9ea42c3dfe
--- /dev/null
+++ b/arch/x86/mm/vmalloc.c
@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * vmalloc.c: x86 arch version of vmalloc.c
+ *
+ * (C) Copyright 2018 Intel Corporation
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; version 2
+ * of the License.
+ */
+
+#include <linux/mm.h>
+#include <linux/set_memory.h>
+#include <linux/vmalloc.h>
+
+static void set_area_direct_np(struct vm_struct *area)
+{
+ int i;
+
+ for (i = 0; i < area->nr_pages; i++)
+ set_pages_np_noflush(area->pages[i], 1);
+}
+
+static void set_area_direct_prw(struct vm_struct *area)
+{
+ int i;
+
+ for (i = 0; i < area->nr_pages; i++)
+ set_pages_p_noflush(area->pages[i], 1);
+}
+
+void arch_vunmap(struct vm_struct *area, int deallocate_pages)
+{
+ int immediate = area->flags & VM_IMMEDIATE_UNMAP;
+ int special = area->flags & VM_HAS_SPECIAL_PERMS;
+
+ /* Unmap from vmalloc area */
+ remove_vm_area(area->addr);
+
+ /* If no need to reset directmap perms, just check if need to flush */
+ if (!(deallocate_pages || special)) {
+ if (immediate)
+ vm_unmap_aliases();
+ return;
+ }
+
+ /* From here we need to make sure to reset the direct map perms */
+
+ /*
+ * If the area being freed does not have any extra capabilities, we can
+ * just reset the directmap to RW before freeing.
+ */
+ if (!immediate) {
+ set_area_direct_prw(area);
+ vm_unmap_aliases();
+ return;
+ }
+
+ /*
+ * If the vm being freed has security sensitive capabilities such as
+ * executable we need to make sure there is no W window on the directmap
+ * before removing the X in the TLB. So we set not present first so we
+ * can flush without any other CPU picking up the mapping. Then we reset
+ * RW+P without a flush, since NP prevented it from being cached by
+ * other cpus.
+ */
+ set_area_direct_np(area);
+ vm_unmap_aliases();
+ set_area_direct_prw(area);
+}
--
2.17.1