Re: RESEND: Re: Problem booting a PowerBook G4 Aluminum after commit cd08f109 with CONFIG_VMAP_STACK=y

From: Christophe Leroy <christophe.leroy@c-s.fr>
To: Larry Finger <Larry.Finger@lwfinger.net>
Cc: "linuxppc-dev@ozlabs.org" <linuxppc-dev@ozlabs.org>
Subject: Re: RESEND: Re: Problem booting a PowerBook G4 Aluminum after commit cd08f109 with CONFIG_VMAP_STACK=y
Date: Sat, 15 Feb 2020 08:55:34 +0100	[thread overview]
Message-ID: <5f4b7426-0989-7723-8993-4a0aaa71b592@c-s.fr> (raw)
In-Reply-To: <04c1c725-6360-1663-c6ae-a4c7611dc385@lwfinger.net>

Le 15/02/2020 à 03:42, Larry Finger a écrit :
> Christophe,
> 
> On 2/14/20 1:35 PM, Christophe Leroy wrote:
>> --- a/arch/powerpc/kernel/head_32.S
>> +++ b/arch/powerpc/kernel/head_32.S
>> @@ -270,6 +270,9 @@ __secondary_hold_acknowledge:
>>    * pointer when we take an exception from supervisor mode.)
>>    *    -- paulus.
>>    */
>> +#ifdef CONFIG_PPC_CHRP
>> +1:    b    machine_check_in_rtas
>> +#endif
>>       . = 0x200
>>       DO_KVM  0x200
>>   MachineCheck:
>> @@ -290,12 +293,9 @@ MachineCheck:
>>   7:    EXCEPTION_PROLOG_2
>>       addi    r3,r1,STACK_FRAME_OVERHEAD
>>   #ifdef CONFIG_PPC_CHRP
>> -    bne    cr1,1f
>> +    bne    cr1,1b
>>   #endif
>>       EXC_XFER_STD(0x200, machine_check_exception)
>> -#ifdef CONFIG_PPC_CHRP
>> -1:    b    machine_check_in_rtas
>> -#endif

I'll need to make it a bit different because it shoehorns into your 
config but won't fit if CONFIG_KVM_BOOK3S_32 is added.

>>
>>   /* Data access exception. */
>>       . = 0x300
> 
> With the above changes and all the other patches applied, the machine 
> finally boots. It is so bloody slow that it takes a long time to do 
> anything, but you finally got all the places that needed patches. I 
> really lost track of how many bugs were fixed in the process, but I can 
> now put that old box aside until time for v5.7.0-rc1. As you can tell, 
> it only gets used to verify that PPC32 is working on real G4 hardware. 
> It has no real value for any other function.

Yes, I don't have a G4 myself but this is so much nested with other 
stuff for the powerpc 83xx than we can't avoid the changes impacting the 
G4 and other hash-MMU based PPC32 allthough the changes I'm doing are 
not targetted at those platform at first. And as the 83xx is a 603 core, 
it is non-hash so all hash related things can't be verified. Plus all 
those small parts like power saving, RTAS, etc... which are more specific.
And checking with all possible options is also not easy.

VMAP-STACK was really a challenging functionnality, I'm happy it made 
its way to mainline though.

> 
> Thanks for the help,

Thanks to you for testing and for your patience.

Christophe