netdev - Re: [PATCH 2/2] arm64: bpf: add extra pass to handle faulty codegen

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Message-ID: <20160115050937.GB52169@ast-mbp.thefacebook.com>
Date:	Thu, 14 Jan 2016 21:09:38 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Zi Shen Lim <zlim.lnx@...il.com>
Cc:	Alexei Starovoitov <ast@...nel.org>,
	Will Deacon <will.deacon@....com>,
	"David S. Miller" <davem@...emloft.net>,
	Catalin Marinas <catalin.marinas@....com>,
	Rabin Vincent <rabin@....in>, netdev@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] arm64: bpf: add extra pass to handle faulty codegen

On Wed, Jan 13, 2016 at 11:33:22PM -0800, Zi Shen Lim wrote:
> Code generation functions in arch/arm64/kernel/insn.c previously
> BUG_ON invalid parameters. Following change of that behavior, now we
> need to handle the error case where AARCH64_BREAK_FAULT is returned.
> 
> Instead of error-handling on every emit() in JIT, we add a new
> validation pass at the end of JIT compilation. There's no point in
> running JITed code at run-time only to trap due to AARCH64_BREAK_FAULT.
> Instead, we drop this failed JIT compilation and allow the system to
> gracefully fallback on the BPF interpreter.
> 
> Signed-off-by: Zi Shen Lim <zlim.lnx@...il.com>
> Suggested-by: Alexei Starovoitov <ast@...nel.org>

Looks good to me.
Acked-by: Alexei Starovoitov <ast@...nel.org>
technically it's a bug fix, though the shift problem is already mitigated.
Will, any comments?