[PATCH] x86/bpf: make arch_bpf_trampoline_size allocate from EXECMEM_MODULE_DATA

[Mike Rapoport]

From: "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx>

Jiri Olsa reports slowdown of tracing_multi benchmark that allocates huge
number of trampolines [1].

The slowdown caused by extra protection changes in execmem_alloc_rw() and
execmem_free().

With ROX caches enabled, all execmem allocations except EXECMEM_MODULE_DATA
are ROX after the allocation. execmem_alloc_rw() temporarily sets them to
W+NX and execmem_free() resets them back to ROX.

The only user of bpf_jit_alloc_exec_rw() is x86::arch_bpf_trampoline_size()
that only needs a temporary writable buffer in the modules address space.

On x86 executable memory and module data are constrained to the same
address range, so x86::arch_bpf_trampoline_size() can directly use
execmem_alloc(EXECMEM_MODULE_DATA)

Replace the call to bpf_jit_alloc_exec_rw() with a call to
execmem_alloc(EXECMEM_MODULE_DATA) in x86::arch_bpf_trampoline_size() and
drop bpf_jit_alloc_exec_rw() helper.

Reported-by: Jiri Olsa <olsajiri@xxxxxxxxx>
Link: https://lore.kernel.org/all/an8r7EODLIL-bZM3@krava
Fixes: f0334294a428 ("bpf, x86: make sure allocation in arch_bpf_trampoline_size() is writable")
Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
---
 arch/x86/net/bpf_jit_comp.c | 8 +++++---
 include/linux/filter.h      | 1 -
 kernel/bpf/core.c           | 5 -----
 3 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index b2feec81e231..7d064d3e2788 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -13,6 +13,7 @@
 #include <linux/bpf_verifier.h>
 #include <linux/memory.h>
 #include <linux/sort.h>
+#include <linux/execmem.h>
 #include <asm/extable.h>
 #include <asm/ftrace.h>
 #include <asm/set_memory.h>
@@ -3706,15 +3707,16 @@ int arch_bpf_trampoline_size(const struct btf_func_model *m, u32 flags,
 	 *
 	 * We cannot use kvmalloc here, because we need image to be in
 	 * module memory range.
-	 * Since it must be writable use bpf_jit_alloc_exec_rw().
+	 * Since it must be writable use execmem_alloc(EXECMEM_MODULE_DATA)
+	 * that returns writable memory in the module address space.
 	 */
-	image = bpf_jit_alloc_exec_rw(PAGE_SIZE);
+	image = execmem_alloc(EXECMEM_MODULE_DATA, PAGE_SIZE);
 	if (!image)
 		return -ENOMEM;
 
 	ret = __arch_prepare_bpf_trampoline(&im, image, image + PAGE_SIZE, image,
 					    m, flags, tnodes, func_addr);
-	bpf_jit_free_exec(image);
+	execmem_free(image);
 	return ret;
 }
 
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 32d5297c557e..14acb2455746 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1333,7 +1333,6 @@ bpf_jit_binary_alloc(unsigned int proglen, u8 **image_ptr,
 void bpf_jit_binary_free(struct bpf_binary_header *hdr);
 u64 bpf_jit_alloc_exec_limit(void);
 void *bpf_jit_alloc_exec(unsigned long size);
-void *bpf_jit_alloc_exec_rw(unsigned long size);
 void bpf_jit_free_exec(void *addr);
 void bpf_jit_free(struct bpf_prog *fp);
 struct bpf_binary_header *
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index e2076667b245..1b89c18cf246 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1128,11 +1128,6 @@ void *bpf_jit_alloc_exec(unsigned long size)
 	return execmem_alloc(EXECMEM_BPF, size);
 }
 
-void *bpf_jit_alloc_exec_rw(unsigned long size)
-{
-	return execmem_alloc_rw(EXECMEM_BPF, size);
-}
-
 void bpf_jit_free_exec(void *addr)
 {
 	execmem_free(addr);

base-commit: 07edbd8fe6416f45e9ba6b0edcd3e40770601ebc
-- 
2.53.0