diff mbox series

[v8,1/4] vmalloc: Add __vmalloc_node_try_addr function

Message ID 20181102192520.4522-2-rick.p.edgecombe@intel.com (mailing list archive)
State New, archived
Headers show
Series KASLR feature to randomize each loadable module | expand

Commit Message

Edgecombe, Rick P Nov. 2, 2018, 7:25 p.m. UTC 
Create __vmalloc_node_try_addr function that tries to allocate at a specific
address without triggering any lazy purging. In order to support this behavior
a try_addr argument was plugged into several of the static helpers.

This also changes logic in __get_vm_area_node to be faster in cases where
allocations fail due to no space, which is a lot more common when trying
specific addresses.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 include/linux/vmalloc.h |   3 +
 mm/vmalloc.c            | 128 +++++++++++++++++++++++++++++-----------
 2 files changed, 95 insertions(+), 36 deletions(-)

Comments

Andrew Morton Nov. 6, 2018, 9:05 p.m. UTC | #1 
On Fri,  2 Nov 2018 12:25:17 -0700 Rick Edgecombe <rick.p.edgecombe@intel.com> wrote:

> Create __vmalloc_node_try_addr function that tries to allocate at a specific
> address without triggering any lazy purging. In order to support this behavior
> a try_addr argument was plugged into several of the static helpers.

Please explain (in the changelog) why lazy purging is considered to be
a problem.  Preferably with some form of measurements, or at least a
hand-wavy guesstimate of the cost.

> This also changes logic in __get_vm_area_node to be faster in cases where
> allocations fail due to no space, which is a lot more common when trying
> specific addresses.
Edgecombe, Rick P Nov. 7, 2018, 8:03 p.m. UTC | #2 
On Tue, 2018-11-06 at 13:05 -0800, Andrew Morton wrote:
> On Fri,  2 Nov 2018 12:25:17 -0700 Rick Edgecombe <rick.p.edgecombe@intel.com>
> wrote:
> 
> > Create __vmalloc_node_try_addr function that tries to allocate at a specific
> > address without triggering any lazy purging. In order to support this
> > behavior
> > a try_addr argument was plugged into several of the static helpers.
> 
> Please explain (in the changelog) why lazy purging is considered to be
> a problem.  Preferably with some form of measurements, or at least a
> hand-wavy guesstimate of the cost.
Sure, Ill update it to be more clear. The problem is that when
__vmalloc_node_range fails to allocate (in this case tries in a single random
spot that doesn't fit), it triggers a purge_vmap_area_lazy and then retries the
allocation in the same spot. It doesn't make as much sense in this case when we
are not trying over a large area. While it will usually not flush the TLB, it
does do extra work every time for an unlikely case in this situation of a lazy
free area blocking the allocation.

The average allocation time in ns for different versions measured by the
included kselftest:

Modules	Vmalloc optimization	No Vmalloc Optimization	Existing Module KASLR
1000	1433			1993			3821
2000	2295			3681			7830
3000	4424			7450			13012
4000	7746			13824			18106
5000	12721			21852			22572
6000	19724			33926			26443
7000	27638			47427			30473
8000	37745			64443			34200

The other optimization is not kmalloc-ing in __get_vm_area_node until after the
address was tried, which IIRC had a smaller but still noticeable performance
boost.

These allocations are not taking very long, but it may show up on systems with
very high usage of the module space (BPF JITs). If the trade-off of touching
vmalloc doesn't seem worth it to people, I'm happy to remove the optimizations.

> > This also changes logic in __get_vm_area_node to be faster in cases where
> > allocations fail due to no space, which is a lot more common when trying
> > specific addresses.
diff mbox series

Patch

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 398e9c95cd61..6eaa89612372 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -82,6 +82,9 @@  extern void *__vmalloc_node_range(unsigned long size, unsigned long align,
 			unsigned long start, unsigned long end, gfp_t gfp_mask,
 			pgprot_t prot, unsigned long vm_flags, int node,
 			const void *caller);
+extern void *__vmalloc_node_try_addr(unsigned long addr, unsigned long size,
+			gfp_t gfp_mask,	pgprot_t prot, unsigned long vm_flags,
+			int node, const void *caller);
 #ifndef CONFIG_MMU
 extern void *__vmalloc_node_flags(unsigned long size, int node, gfp_t flags);
 static inline void *__vmalloc_node_flags_caller(unsigned long size, int node,
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a728fc492557..8d01f503e20d 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -326,6 +326,9 @@  EXPORT_SYMBOL(vmalloc_to_pfn);
 #define VM_LAZY_FREE	0x02
 #define VM_VM_AREA	0x04
 
+#define VMAP_MAY_PURGE	0x2
+#define VMAP_NO_PURGE	0x1
+
 static DEFINE_SPINLOCK(vmap_area_lock);
 /* Export for kexec only */
 LIST_HEAD(vmap_area_list);
@@ -402,12 +405,12 @@  static BLOCKING_NOTIFIER_HEAD(vmap_notify_list);
 static struct vmap_area *alloc_vmap_area(unsigned long size,
 				unsigned long align,
 				unsigned long vstart, unsigned long vend,
-				int node, gfp_t gfp_mask)
+				int node, gfp_t gfp_mask, int try_purge)
 {
 	struct vmap_area *va;
 	struct rb_node *n;
 	unsigned long addr;
-	int purged = 0;
+	int purged = try_purge & VMAP_NO_PURGE;
 	struct vmap_area *first;
 
 	BUG_ON(!size);
@@ -860,7 +863,7 @@  static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)
 
 	va = alloc_vmap_area(VMAP_BLOCK_SIZE, VMAP_BLOCK_SIZE,
 					VMALLOC_START, VMALLOC_END,
-					node, gfp_mask);
+					node, gfp_mask, VMAP_MAY_PURGE);
 	if (IS_ERR(va)) {
 		kfree(vb);
 		return ERR_CAST(va);
@@ -1170,8 +1173,9 @@  void *vm_map_ram(struct page **pages, unsigned int count, int node, pgprot_t pro
 		addr = (unsigned long)mem;
 	} else {
 		struct vmap_area *va;
-		va = alloc_vmap_area(size, PAGE_SIZE,
-				VMALLOC_START, VMALLOC_END, node, GFP_KERNEL);
+		va = alloc_vmap_area(size, PAGE_SIZE, VMALLOC_START,
+					VMALLOC_END, node, GFP_KERNEL,
+					VMAP_MAY_PURGE);
 		if (IS_ERR(va))
 			return NULL;
 
@@ -1372,7 +1376,8 @@  static void clear_vm_uninitialized_flag(struct vm_struct *vm)
 
 static struct vm_struct *__get_vm_area_node(unsigned long size,
 		unsigned long align, unsigned long flags, unsigned long start,
-		unsigned long end, int node, gfp_t gfp_mask, const void *caller)
+		unsigned long end, int node, gfp_t gfp_mask, int try_purge,
+		const void *caller)
 {
 	struct vmap_area *va;
 	struct vm_struct *area;
@@ -1386,16 +1391,17 @@  static struct vm_struct *__get_vm_area_node(unsigned long size,
 		align = 1ul << clamp_t(int, get_count_order_long(size),
 				       PAGE_SHIFT, IOREMAP_MAX_ORDER);
 
-	area = kzalloc_node(sizeof(*area), gfp_mask & GFP_RECLAIM_MASK, node);
-	if (unlikely(!area))
-		return NULL;
-
 	if (!(flags & VM_NO_GUARD))
 		size += PAGE_SIZE;
 
-	va = alloc_vmap_area(size, align, start, end, node, gfp_mask);
-	if (IS_ERR(va)) {
-		kfree(area);
+	va = alloc_vmap_area(size, align, start, end, node, gfp_mask,
+				try_purge);
+	if (IS_ERR(va))
+		return NULL;
+
+	area = kzalloc_node(sizeof(*area), gfp_mask & GFP_RECLAIM_MASK, node);
+	if (unlikely(!area)) {
+		free_vmap_area(va);
 		return NULL;
 	}
 
@@ -1408,7 +1414,8 @@  struct vm_struct *__get_vm_area(unsigned long size, unsigned long flags,
 				unsigned long start, unsigned long end)
 {
 	return __get_vm_area_node(size, 1, flags, start, end, NUMA_NO_NODE,
-				  GFP_KERNEL, __builtin_return_address(0));
+				  GFP_KERNEL, VMAP_MAY_PURGE,
+				  __builtin_return_address(0));
 }
 EXPORT_SYMBOL_GPL(__get_vm_area);
 
@@ -1417,7 +1424,7 @@  struct vm_struct *__get_vm_area_caller(unsigned long size, unsigned long flags,
 				       const void *caller)
 {
 	return __get_vm_area_node(size, 1, flags, start, end, NUMA_NO_NODE,
-				  GFP_KERNEL, caller);
+				  GFP_KERNEL, VMAP_MAY_PURGE, caller);
 }
 
 /**
@@ -1432,7 +1439,7 @@  struct vm_struct *__get_vm_area_caller(unsigned long size, unsigned long flags,
 struct vm_struct *get_vm_area(unsigned long size, unsigned long flags)
 {
 	return __get_vm_area_node(size, 1, flags, VMALLOC_START, VMALLOC_END,
-				  NUMA_NO_NODE, GFP_KERNEL,
+				  NUMA_NO_NODE, GFP_KERNEL, VMAP_MAY_PURGE,
 				  __builtin_return_address(0));
 }
 
@@ -1440,7 +1447,8 @@  struct vm_struct *get_vm_area_caller(unsigned long size, unsigned long flags,
 				const void *caller)
 {
 	return __get_vm_area_node(size, 1, flags, VMALLOC_START, VMALLOC_END,
-				  NUMA_NO_NODE, GFP_KERNEL, caller);
+				  NUMA_NO_NODE, GFP_KERNEL, VMAP_MAY_PURGE,
+				  caller);
 }
 
 /**
@@ -1709,26 +1717,10 @@  static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 	return NULL;
 }
 
-/**
- *	__vmalloc_node_range  -  allocate virtually contiguous memory
- *	@size:		allocation size
- *	@align:		desired alignment
- *	@start:		vm area range start
- *	@end:		vm area range end
- *	@gfp_mask:	flags for the page level allocator
- *	@prot:		protection mask for the allocated pages
- *	@vm_flags:	additional vm area flags (e.g. %VM_NO_GUARD)
- *	@node:		node to use for allocation or NUMA_NO_NODE
- *	@caller:	caller's return address
- *
- *	Allocate enough pages to cover @size from the page level
- *	allocator with @gfp_mask flags.  Map them into contiguous
- *	kernel virtual space, using a pagetable protection of @prot.
- */
-void *__vmalloc_node_range(unsigned long size, unsigned long align,
+static void *__vmalloc_node_range_opts(unsigned long size, unsigned long align,
 			unsigned long start, unsigned long end, gfp_t gfp_mask,
 			pgprot_t prot, unsigned long vm_flags, int node,
-			const void *caller)
+			int try_purge, const void *caller)
 {
 	struct vm_struct *area;
 	void *addr;
@@ -1739,7 +1731,8 @@  void *__vmalloc_node_range(unsigned long size, unsigned long align,
 		goto fail;
 
 	area = __get_vm_area_node(size, align, VM_ALLOC | VM_UNINITIALIZED |
-				vm_flags, start, end, node, gfp_mask, caller);
+				vm_flags, start, end, node, gfp_mask,
+				try_purge, caller);
 	if (!area)
 		goto fail;
 
@@ -1764,6 +1757,69 @@  void *__vmalloc_node_range(unsigned long size, unsigned long align,
 	return NULL;
 }
 
+/**
+ *	__vmalloc_node_range  -  allocate virtually contiguous memory
+ *	@size:		allocation size
+ *	@align:		desired alignment
+ *	@start:		vm area range start
+ *	@end:		vm area range end
+ *	@gfp_mask:	flags for the page level allocator
+ *	@prot:		protection mask for the allocated pages
+ *	@vm_flags:	additional vm area flags (e.g. %VM_NO_GUARD)
+ *	@node:		node to use for allocation or NUMA_NO_NODE
+ *	@caller:	caller's return address
+ *
+ *	Allocate enough pages to cover @size from the page level
+ *	allocator with @gfp_mask flags.  Map them into contiguous
+ *	kernel virtual space, using a pagetable protection of @prot.
+ */
+void *__vmalloc_node_range(unsigned long size, unsigned long align,
+			unsigned long start, unsigned long end, gfp_t gfp_mask,
+			pgprot_t prot, unsigned long vm_flags, int node,
+			const void *caller)
+{
+	return __vmalloc_node_range_opts(size, align, start, end, gfp_mask,
+					prot, vm_flags, node, VMAP_MAY_PURGE,
+					caller);
+}
+
+/**
+ *	__vmalloc_try_addr  -  try to alloc at a specific address
+ *	@addr:		address to try
+ *	@size:		size to try
+ *	@gfp_mask:	flags for the page level allocator
+ *	@prot:		protection mask for the allocated pages
+ *	@vm_flags:	additional vm area flags (e.g. %VM_NO_GUARD)
+ *	@node:		node to use for allocation or NUMA_NO_NODE
+ *	@caller:	caller's return address
+ *
+ *	Try to allocate at the specific address. If it succeeds the address is
+ *	returned. If it fails NULL is returned.  It will not try to purge lazy
+ *	free vmap areas in order to fit.
+ */
+void *__vmalloc_node_try_addr(unsigned long addr, unsigned long size,
+			gfp_t gfp_mask,	pgprot_t prot, unsigned long vm_flags,
+			int node, const void *caller)
+{
+	unsigned long addr_end;
+	unsigned long vsize = PAGE_ALIGN(size);
+
+	if (!vsize || (vsize >> PAGE_SHIFT) > totalram_pages)
+		return NULL;
+
+	if (!(vm_flags & VM_NO_GUARD))
+		vsize += PAGE_SIZE;
+
+	addr_end = addr + vsize;
+
+	if (addr > addr_end)
+		return NULL;
+
+	return __vmalloc_node_range_opts(size, 1, addr, addr_end,
+				gfp_mask | __GFP_NOWARN, prot, vm_flags, node,
+				VMAP_NO_PURGE, caller);
+}
+
 /**
  *	__vmalloc_node  -  allocate virtually contiguous memory
  *	@size:		allocation size