From: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>
To: "Kumar Kartikeya Dwivedi" <memxor@gmail.com>, <bpf@vger.kernel.org>
Cc: "Andrii Nakryiko" <andrii@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Eduard Zingerman" <eddyz87@gmail.com>,
"Emil Tsalapatis" <emil@etsalapatis.com>,
"Tejun Heo" <tj@kernel.org>, <kkd@meta.com>,
<kernel-team@meta.com>
Subject: Re: [PATCH bpf-next v1 12/18] bpf: Size the per-frame verifier structures for a 2 KiB stack
Date: Wed, 23 Sep 2026 22:55:46 +0000 [thread overview]
Message-ID: <DLN2ENBJI5F7.1S4FUJ3ROP51V@gmail.com> (raw)
In-Reply-To: <20260923191139.2816206-13-memxor@gmail.com>
On Wed, Sep 23, 2026 at 09:11 PM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote:
> -#define FRAME_HALF_SPIS (MAX_BPF_STACK / BPF_HALF_REG_SIZE)
> +#define FRAME_HALF_SPIS (MAX_BPF_STACK_JIT / BPF_HALF_REG_SIZE)
MAX_ARG_SPILL_SLOTS in liveness.c is still 64.
fp_off_to_slot() returns -1 for anything below fp-512, so
r6 = *(u64 *)(r10 - 520)
makes r6 ARG_IMPRECISE in fill_from_stack() no matter what was
spilled there. The next load or store through r6 goes to
record_imprecise() and marks the whole stack of every frame as read.
A prog that keeps spills below fp-512 gets no help from liveness
and all of its frames carry 8 word masks.
The numbers in the cover letter are for selftests that fit in 512.
Pls share veristat numbers for progs that use more than that.
next prev parent reply other threads:[~2026-09-23 22:55 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-23 19:11 [PATCH bpf-next v1 00/18] Raise BPF program stack size to 2KiB Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 01/18] bpf: Add accessors for verifier stack slots Kumar Kartikeya Dwivedi
2026-09-23 19:57 ` bot+bpf-ci
2026-09-23 20:04 ` Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 02/18] bpf: Widen the stack slot index in the jump history Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 03/18] bpf: Store linked registers in the jump history as an array Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 04/18] bpf: Track backtracking stack slots with bitmaps Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 05/18] bpf: Track scratched stack slots with a bitmap Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 06/18] bpf: Treat unknown-size stack reads as reaching the frame top Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 07/18] bpf: Size liveness stack masks by the stack each frame uses Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 08/18] bpf: Grow the verifier id scratch on demand Kumar Kartikeya Dwivedi
2026-09-23 19:24 ` sashiko-bot
2026-09-23 19:29 ` Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 09/18] selftests/bpf: Cover the tail call caller stack depth limit Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 10/18] selftests/bpf: Check that narrow stack stores define no slot Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 11/18] selftests/bpf: Check liveness merge of masks with different widths Kumar Kartikeya Dwivedi
2026-09-23 19:26 ` sashiko-bot
2026-09-23 19:29 ` Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 12/18] bpf: Size the per-frame verifier structures for a 2 KiB stack Kumar Kartikeya Dwivedi
2026-09-23 20:12 ` bot+bpf-ci
2026-09-23 20:27 ` Kumar Kartikeya Dwivedi
2026-09-23 22:55 ` Alexei Starovoitov [this message]
2026-09-23 19:11 ` [PATCH bpf-next v1 13/18] bpf: Bound program stack use by a per-program limit Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 14/18] selftests/bpf: Add load conditions on the program stack limit Kumar Kartikeya Dwivedi
2026-09-23 20:12 ` bot+bpf-ci
2026-09-23 20:27 ` Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 15/18] selftests/bpf: Give the 512-byte stack boundary tests a 2 KiB twin Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 16/18] bpf, x86: Allow programs 2 KiB of stack Kumar Kartikeya Dwivedi
2026-09-23 20:12 ` bot+bpf-ci
2026-09-23 20:28 ` Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 17/18] bpf, arm64: " Kumar Kartikeya Dwivedi
2026-09-23 19:11 ` [PATCH bpf-next v1 18/18] selftests/bpf: Test the 2 KiB stack budget Kumar Kartikeya Dwivedi
2026-09-23 20:12 ` bot+bpf-ci
2026-09-23 20:28 ` Kumar Kartikeya Dwivedi
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