From: marc.zyngier@arm•com (Marc Zyngier)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v2 0/4] arm64: alternative patching rework
Date: Wed, 03 Jun 2015 14:36:09 +0100 [thread overview]
Message-ID: <556F02C9.9020706@arm.com> (raw)
In-Reply-To: <20150602175902.GF3080@e104818-lin.cambridge.arm.com>
Hi Catalin,
On 02/06/15 18:59, Catalin Marinas wrote:
> On Tue, Jun 02, 2015 at 06:47:15PM +0100, Catalin Marinas wrote:
>> On Mon, Jun 01, 2015 at 10:47:38AM +0100, Marc Zyngier wrote:
>>> The current alternative instruction framework is not kind to branches,
>>> potentially leading to all kind of hacks in the code that uses
>>> alternatives. This series expands it to deal with immediate and
>>> conditional branches.
>>>
>>> This is a rewrite of fef7f2b20103, which got reverted in b9a95e85bbc
>>> as it was breaking unsuspecting branches inside an alternate
>>> sequence. It now also deals with conditional branches (instead of just
>>> asserting a BUG).
>>>
>>> Another nit is addressed by the last patch, where GAS gets confused by
>>> the combinaison of a .inst directive (as used by the msr_s/mrs_s
>>> pseudo-instruction), a label, and a .if directive evaluating said
>>> label. As this is exactly what the alternative framework uses to
>>> detect length mismatch, this patch reverts to using a pair of .org
>>> directives in a creative way. To make this a bit easier,
>>> alternative-asm.h is folded into alternative.h.
>>>
>>> This has been tested on v4.1-rc5.
>>>
>>> Marc Zyngier (4):
>>> arm64: insn: Add aarch64_{get,set}_branch_offset
>>> arm64: alternative: Allow immediate branch as alternative instruction
>>> arm64: alternative: Merge alternative-asm.h into alternative.h
>>> arm64: alternative: Work around .inst assembler bugs
>>
>> Applied, thanks.
>
> Applied, but not pushed out yet. Testing on Juno gives:
>
> alternatives: patching kernel code
> BUG: failure at /work/Linux/linux-2.6-aarch64/arch/arm64/kernel/alternative.c:59/branch_insn_requires_update()!
> Kernel panic - not syncing: BUG!
> CPU: 0 PID: 10 Comm: migration/0 Not tainted 4.1.0-rc4+ #224
> Hardware name: Juno (DT)
> Call trace:
> [<ffffffc00008992c>] dump_backtrace+0x0/0x11c
> [<ffffffc000089a58>] show_stack+0x10/0x1c
> [<ffffffc0005b49b4>] dump_stack+0x88/0xc8
> [<ffffffc0005b38a8>] panic+0xe0/0x220
> [<ffffffc00008e3b0>] __apply_alternatives+0x1ac/0x1cc
> [<ffffffc000123aa8>] multi_cpu_stop+0xf8/0x120
> [<ffffffc000123d60>] cpu_stopper_thread+0xb0/0x148
> [<ffffffc0000d12ec>] smpboot_thread_fn+0x150/0x274
> [<ffffffc0000cdedc>] kthread+0xd8/0xf0
> SMP: failed to stop secondary CPUs
>
>
> I haven't investigated yet, I'll have a look tomorrow.
I reproduced this. Two issues:
- the workaround for CONFIG_ARM64_ERRATUM_845719 is written with two
alternate sequences, and the first one branches in to the second.
Exactly what this series disallows... I'll post a rewrite of this
sequence in a minute.
- there is a small bug that the above also triggers, as it branches
just *after* the last instruction of the sequence. This doesn't
generate any relocation problem, and can be accepted. Can you fold the
patchlet below into the second patch of the series?
diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c
index df4bf15..221b983 100644
--- a/arch/arm64/kernel/alternative.c
+++ b/arch/arm64/kernel/alternative.c
@@ -49,7 +49,7 @@ static bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc)
return 1;
replptr = (unsigned long)ALT_REPL_PTR(alt);
- if (pc >= replptr && pc < (replptr + alt->alt_len))
+ if (pc >= replptr && pc <= (replptr + alt->alt_len))
return 0;
/*
Thanks,
M.
--
Jazz is not dead. It just smells funny...
prev parent reply other threads:[~2015-06-03 13:36 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-01 9:47 [PATCH v2 0/4] arm64: alternative patching rework Marc Zyngier
2015-06-01 9:47 ` [PATCH v2 1/4] arm64: insn: Add aarch64_{get,set}_branch_offset Marc Zyngier
2015-06-01 9:47 ` [PATCH v2 2/4] arm64: alternative: Allow immediate branch as alternative instruction Marc Zyngier
2015-06-01 9:47 ` [PATCH v2 3/4] arm64: alternative: Merge alternative-asm.h into alternative.h Marc Zyngier
2015-06-01 9:47 ` [PATCH v2 4/4] arm64: alternative: Work around .inst assembler bugs Marc Zyngier
2015-06-02 17:47 ` [PATCH v2 0/4] arm64: alternative patching rework Catalin Marinas
2015-06-02 17:59 ` Catalin Marinas
2015-06-03 13:36 ` Marc Zyngier [this message]
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