Re: [EXTERNAL] Re: [PULL 18/23] accel/tcg: re-factor non-RAM execution code

From: "Cédric Le Goater" <clg@kaod.org>
To: "Alex Bennée" <alex.bennee@linaro.org>
Cc: "Peter Maydell" <peter.maydell@linaro.org>,
	"Richard Henderson" <richard.henderson@linaro.org>,
	"QEMU Developers" <qemu-devel@nongnu.org>,
	"Philippe Mathieu-Daudé" <f4bug@amsat.org>,
	qemu-arm <qemu-arm@nongnu.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>
Subject: Re: [EXTERNAL] Re: [PULL 18/23] accel/tcg: re-factor non-RAM execution code
Date: Fri, 16 Apr 2021 12:14:13 +0200	[thread overview]
Message-ID: <9c14e634-cd3e-d984-b24f-2abc99536aa0@kaod.org> (raw)
In-Reply-To: <8735vqlhdm.fsf@linaro.org>

On 4/16/21 11:14 AM, Alex Bennée wrote:
> 
> Cédric Le Goater <clg@kaod.org> writes:
> 
>> On 4/15/21 7:34 PM, Peter Maydell wrote:
>>> On Thu, 15 Apr 2021 at 18:18, Cédric Le Goater <clg@kaod.org> wrote:
>>>>
>>>> On 4/15/21 5:55 PM, Philippe Mathieu-Daudé wrote:
>>>>> On 4/15/21 4:54 PM, Peter Maydell wrote:
>>>>>> On Thu, 15 Apr 2021 at 15:32, Alex Bennée <alex.bennee@linaro.org> wrote:
>>>>>>> --8<---------------cut here---------------start------------->8---
>>>>>>> accel/tcg: avoid re-translating one-shot instructions
>>>>>>>
>>>>>>> By definition a single instruction is capable of being an IO
>>>>>>> instruction. This avoids a problem of triggering a cpu_io_recompile on
>>>>>>> a non-cached translation which would only do exactly this anyway.
>>>>>>>
>>>>>>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>>>>>>>
>>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>> accel/tcg/translate-all.c | 2 +-
>>>>>>>
>>>>>>> modified   accel/tcg/translate-all.c
>>>>>>> @@ -1863,7 +1863,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>>>>>>>
>>>>>>>      if (phys_pc == -1) {
>>>>>>>          /* Generate a one-shot TB with 1 insn in it */
>>>>>>> -        cflags = (cflags & ~CF_COUNT_MASK) | 1;
>>>>>>> +        cflags = (cflags & ~CF_COUNT_MASK) | CF_LAST_IO | 1;
>>>>>>>      }
>>>>>>>
>>>>>>>      max_insns = cflags & CF_COUNT_MASK;
>>>>>>> --8<---------------cut here---------------end--------------->8---
>>>>>>
>>>>>> Yes, this fixes the problem. Do we want to put this in for 6.0? My
>>>>>> feeling is that executing from non-RAM is pretty niche, so maybe
>>>>>> if we need an rc4 anyway, but this isn't important enough to cause an
>>>>>> rc4 itself.
>>>>>
>>>>> Isn't it the default for Aspeed machines (with U-Boot)? (Cc'ing Cédric).
>>>>
>>>> You need to set the 'execute-in-place' machine option to load/execute the
>>>> instructions from the AHB window of CE0. It's not on by default because
>>>> boot can be really slow with some recent u-boot which heavily trash the TBs.
>>>>
>>>> But this seems to work fine with -rc3.
>>>
>>> Triggering the bug requires both execute-in-place and -icount -- did
>>> you test with -icount enabled?
>>
>> It crashes.
> 
> 
> Without the above patch? I've re-posted as a proper patch here:
> 
>   Subject: [RFC PATCH] accel/tcg: avoid re-translating one-shot instructions
>   Date: Thu, 15 Apr 2021 17:24:53 +0100
>   Message-Id: <20210415162454.22056-1-alex.bennee@linaro.org>
> 

This patch does not fix the crash for the aspeed machines.

C.