Re: [PATCH v1 1/2] target/ppc: Fix decrementer time underflow and infinite timer loop

[Daniel Henrique Barboza <danielhb413@gmail.com>]

On 6/7/23 06:26, Michael Tokarev wrote:
> 30.05.2023 16:12, Nicholas Piggin wrote:
>> It is possible to store a very large value to the decrementer that it
>> does not raise the decrementer exception so the timer is scheduled, but
>> the next time value wraps and is treated as in the past.
>>
>> This can occur if (u64)-1 is stored on a zero-triggered exception, or
>> (u64)-1 is stored twice on an underflow-triggered exception, for
>> example.
>>
>> If such a value is set in DECAR, it gets stored to the decrementer by
>> the timer function, which then immediately causes another timer, which
>> hangs QEMU.
>>
>> Clamp the decrementer to the implemented width, and use that as the
>> value for the timer calculation, effectively preventing this overflow.
>>
>> Reported-by: sdicaro@DDCI.com
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>> sdicaro@DDCI.com debugged and reported this, I just changed their fix
>> to extract variable bits so it works with large decrementer. So most
>> of the credit goes to them.
>>
>> Thanks,
>> Nick
>>
>>   hw/ppc/ppc.c | 2 ++
>>   1 file changed, 2 insertions(+)
> 
> Is it a -stable material?  From the description it smells like it is.

Feel free to pick it for -stable.  Thanks,

Daniel

> 
> Thanks,
> 
> /mjt
>