Re: [PATCH] pnv_lpc: disable reentrancy detection for lpc-hc

[Frederic Barrat <fbarrat@linux.ibm.com>]

On 11/05/2023 11:15, Alexander Bulekov wrote:
> On 230511 1104, Cédric Le Goater wrote:
>> Hello Alexander
>>
>> On 5/11/23 10:53, Alexander Bulekov wrote:
>>> As lpc-hc is designed for re-entrant calls from xscom, mark it
>>> re-entrancy safe.
>>>
>>> Reported-by: Thomas Huth <thuth@redhat.com>
>>> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
>>> ---
>>>    hw/ppc/pnv_lpc.c | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/hw/ppc/pnv_lpc.c b/hw/ppc/pnv_lpc.c
>>> index 01f44c19eb..67fd049a7f 100644
>>> --- a/hw/ppc/pnv_lpc.c
>>> +++ b/hw/ppc/pnv_lpc.c
>>> @@ -738,6 +738,8 @@ static void pnv_lpc_realize(DeviceState *dev, Error **errp)
>>>                                    &lpc->opb_master_regs);
>>>        memory_region_init_io(&lpc->lpc_hc_regs, OBJECT(dev), &lpc_hc_ops, lpc,
>>>                              "lpc-hc", LPC_HC_REGS_OPB_SIZE);
>>> +    /* xscom writes to lpc-hc. As such mark lpc-hc re-entrancy safe */
>>> +    lpc->lpc_hc_regs.disable_reentrancy_guard = true;
>>>        memory_region_add_subregion(&lpc->opb_mr, LPC_HC_REGS_OPB_ADDR,
>>>                                    &lpc->lpc_hc_regs);
>>
>> The warning changed :
>>
>>    qemu-system-ppc64: warning: Blocked re-entrant IO on MemoryRegion: lpc-opb-master at addr: 0x8
>>
>> I will take a look unless you know exactly what to do.
>>
> 
> That does not show up for me with "./qemu-system-ppc64 -M powernv8"
> Do I need to boot a kernel to see the message?
> 
> I was worried that there might be other re-entrant IO in this device.
> Maybe there should be a way to just mark the whole device re-entrancy
> safe.

Hello,

I was also started hitting it, with machine powernv10. And indeed, 
disabling the check on both lpc_hc_regs and opb_master_regs should be 
all we need (and it's working fine for me).

   Fred