Patch "bpf, x64: increase number of passes" has been added to the 4.15-stable tree

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

bpf, x64: increase number of passes

to the 4.15-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:
bpf-x64-increase-number-of-passes.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Daniel Borkmann <[email protected]>
Date: Wed, 7 Mar 2018 22:10:01 +0100
Subject: bpf, x64: increase number of passes

From: Daniel Borkmann <[email protected]>

commit 6007b080d2e2adb7af22bf29165f0594ea12b34c upstream.

In Cilium some of the main programs we run today are hitting 9 passes on x64's JIT compiler, and we've had cases already where we surpassed the limit where the JIT then punts the program to the interpreter instead, leading to insertion failures due to CONFIG_BPF_JIT_ALWAYS_ON or insertion failures due to the prog array owner being JITed but the program to insert not (both must have the same JITed/non-JITed property).

One concrete case the program image shrunk from 12,767 bytes down to 10,288 bytes where the image converged after 16 steps. I've measured that this took 340us in the JIT until it converges on my i7-6600U. Thus, increase the original limit we had from day one where the JIT covered cBPF only back then before we run into the case (as similar with the complexity limit) where we trip over this and hit program rejections. Also add a cond_resched() into the compilation loop, the JIT process runs without any locks and may sleep anyway.

---
 arch/x86/net/bpf_jit_comp.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -1156,7 +1156,7 @@ struct bpf_prog *bpf_int_jit_compile(str
 	 * may converge on the last pass. In such case do one more
 	 * pass to emit the final image
 	 */
-	for (pass = 0; pass < 10 || image; pass++) {
+	for (pass = 0; pass < 20 || image; pass++) {
 		proglen = do_jit(prog, addrs, image, oldproglen, &ctx);
 		if (proglen <= 0) {
 			image = NULL;

@@ -1183,6 +1183,7 @@ struct bpf_prog *bpf_int_jit_compile(str
 			}
 		}
 		oldproglen = proglen;
+		cond_resched();
 	}
 
 	if (bpf_jit_enable > 1)

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/trace-bpf-remove-helper-bpf_perf_prog_read_value-from-tracepoint-type-programs.patch queue-4.15/kbuild-disable-clang-s-default-use-of-fmerge-all-constants.patch queue-4.15/bpf-skip-unnecessary-capability-check.patch queue-4.15/bpf-x64-increase-number-of-passes.patch