[OpenBIOS] [PATCH] ppc: use rfid when running under a CPU from the 970 family.

[Alexander Graf]

On 06/20/2016 03:26 PM, Alexander Graf wrote:
> On 06/20/2016 02:59 PM, Cédric Le Goater wrote:
>> On 06/20/2016 11:49 AM, Mark Cave-Ayland wrote:
>>> On 20/06/16 10:33, Alexander Graf wrote:
>>>
>>>> On 06/20/2016 11:32 AM, Cédric Le Goater wrote:
>>>>> On 06/20/2016 09:39 AM, Alexander Graf wrote:
>>>>>> On 20.06.16 09:34, Cédric Le Goater wrote:
>>>>>>> A recent attempt to restrict the use of rfi to 64bit cpus in qemu
>>>>>>> broke 32bit OpenBIOS when run under a 970.
>>>>>>>
>>>>>>> This is adding a dynamic check on the pvr to choose between rfi and
>>>>>>> rfid. Only the 970 family is supported.
>>>>>>>
>>>>>>> Signed-off-by: Cédric Le Goater <clg at kaod.org>
>>>>>>> ---
>>>>>>>
>>>>>>>    Tested on qemu.
>>>>>>>
>>>>>>>    arch/ppc/qemu/start.S |   25 +++++++++++++++++++++++--
>>>>>>>    arch/ppc/start.S      |   25 +++++++++++++++++++++++--
>>>>>>>    2 files changed, 46 insertions(+), 4 deletions(-)
>>>>>>>
>>>>>>> Index: openbios.git/arch/ppc/qemu/start.S
>>>>>>> ===================================================================
>>>>>>> --- openbios.git.orig/arch/ppc/qemu/start.S
>>>>>>> +++ openbios.git/arch/ppc/qemu/start.S
>>>>>>> @@ -27,6 +27,27 @@
>>>>>>>      #ifdef CONFIG_PPC_64BITSUPPORT
>>>>>>>    +/* When running on ppc64, we cannot use rfi anymore. Let's 
>>>>>>> try to
>>>>>>> + * catch which cpu we are running on and act accordingly. This is
>>>>>>> + * for 970s only.
>>>>>> Do you think you could move the check into the cpu init function 
>>>>>> and use
>>>>>> a global variable / live patching instead? I don't remember if we 
>>>>>> need
>>>>>> to handle any faults before we reach that path.
>>>>> So we get an ISI really early, when returning from setup_mmu(), 
>>>>> which is
>>>>> the first call in _entry.
>>>> Ok, can we add the check there?
>>> Bear in mind that the code for entry/context switching has been 
>>> reworked
>>> pending commit whilst we switch the OpenBIOS repository over from 
>>> SVN to
>>> git. The relevant commits are here:
>>> https://www.coreboot.org/pipermail/openbios/2016-May/009395.html.
>>>
>>> So please consider OpenBIOS git master plus the patchset above to be 
>>> the
>>> latest code.
>> OK. The first version applies fine. I pushed everything here :
>>
>>     https://github.com/legoater/openbios/commits/master
>>
>> I am still looking at what Alex is asking for : a global variable doing
>> live patching for rfi.
>
> It's not both - it's either or :).
>
> So either you define a global variable that we can just read from to 
> determine whether we do rfi or rfid or we live patch. Looking at the 
> code, it's probably easiest to live patch even. Just call a function 
> from setup_mmu() that checks PVR and if it's 64bit, loops through (0x0 
> .. 0x1000) in 32bit steps and checks if *p == INST_RFI. If so, replace 
> with INST_RFID and flush the cache.

... unless we're still running from ROM at that point. Then it gets 
tricky :).


Alex