Patch "x86: bpf_jit: small optimization in emit_bpf_tail_call()" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    x86: bpf_jit: small optimization in emit_bpf_tail_call()

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-bpf_jit-small-optimization-in-emit_bpf_tail_call.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Thu Feb  1 09:05:44 CET 2018
From: Daniel Borkmann <daniel@iogearbox.net>
Date: Tue, 30 Jan 2018 03:37:39 +0100
Subject: x86: bpf_jit: small optimization in emit_bpf_tail_call()
To: gregkh@linuxfoundation.org
Cc: ast@kernel.org, daniel@iogearbox.net, stable@vger.kernel.org, Eric Dumazet <edumazet@google.com>, "David S . Miller" <davem@davemloft.net>
Message-ID: <e0ee628ad21177055e3bad4cea8995f7d66b11c0.1517279268.git.daniel@iogearbox.net>

From: Eric Dumazet <edumazet@google.com>

[ upstream commit 84ccac6e7854ebbfb56d2fc6d5bef9be49bb304c ]

Saves 4 bytes replacing following instructions :

lea rax, [rsi + rdx * 8 + offsetof(...)]
mov rax, qword ptr [rax]
cmp rax, 0

by :

mov rax, [rsi + rdx * 8 + offsetof(...)]
test rax, rax

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/net/bpf_jit_comp.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -269,7 +269,7 @@ static void emit_bpf_tail_call(u8 **ppro
 	EMIT4(0x48, 0x8B, 0x46,                   /* mov rax, qword ptr [rsi + 16] */
 	      offsetof(struct bpf_array, map.max_entries));
 	EMIT3(0x48, 0x39, 0xD0);                  /* cmp rax, rdx */
-#define OFFSET1 47 /* number of bytes to jump */
+#define OFFSET1 43 /* number of bytes to jump */
 	EMIT2(X86_JBE, OFFSET1);                  /* jbe out */
 	label1 = cnt;
 
@@ -278,21 +278,20 @@ static void emit_bpf_tail_call(u8 **ppro
 	 */
 	EMIT2_off32(0x8B, 0x85, -STACKSIZE + 36); /* mov eax, dword ptr [rbp - 516] */
 	EMIT3(0x83, 0xF8, MAX_TAIL_CALL_CNT);     /* cmp eax, MAX_TAIL_CALL_CNT */
-#define OFFSET2 36
+#define OFFSET2 32
 	EMIT2(X86_JA, OFFSET2);                   /* ja out */
 	label2 = cnt;
 	EMIT3(0x83, 0xC0, 0x01);                  /* add eax, 1 */
 	EMIT2_off32(0x89, 0x85, -STACKSIZE + 36); /* mov dword ptr [rbp - 516], eax */
 
 	/* prog = array->ptrs[index]; */
-	EMIT4_off32(0x48, 0x8D, 0x84, 0xD6,       /* lea rax, [rsi + rdx * 8 + offsetof(...)] */
+	EMIT4_off32(0x48, 0x8B, 0x84, 0xD6,       /* mov rax, [rsi + rdx * 8 + offsetof(...)] */
 		    offsetof(struct bpf_array, ptrs));
-	EMIT3(0x48, 0x8B, 0x00);                  /* mov rax, qword ptr [rax] */
 
 	/* if (prog == NULL)
 	 *   goto out;
 	 */
-	EMIT4(0x48, 0x83, 0xF8, 0x00);            /* cmp rax, 0 */
+	EMIT3(0x48, 0x85, 0xC0);		  /* test rax,rax */
 #define OFFSET3 10
 	EMIT2(X86_JE, OFFSET3);                   /* je out */
 	label3 = cnt;


Patches currently in stable-queue which might be from daniel@iogearbox.net are

queue-4.4/bpf-fix-branch-pruning-logic.patch
queue-4.4/bpf-avoid-false-sharing-of-map-refcount-with-max_entries.patch
queue-4.4/x86-bpf_jit-small-optimization-in-emit_bpf_tail_call.patch
queue-4.4/bpf-reject-stores-into-ctx-via-st-and-xadd.patch
queue-4.4/bpf-fix-32-bit-divide-by-zero.patch
queue-4.4/bpf-fix-bpf_tail_call-x64-jit.patch
queue-4.4/bpf-arsh-is-not-supported-in-32-bit-alu-thus-reject-it.patch
queue-4.4/bpf-fix-divides-by-zero.patch
queue-4.4/bpf-introduce-bpf_jit_always_on-config.patch