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

From: Cédric Le Goater
Subject: Re: [PATCH] pnv_lpc: disable reentrancy detection for lpc-hc
Date: Fri, 26 May 2023 09:37:38 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0

On 5/26/23 09:06, Thomas Huth wrote:
On 15/05/2023 14.48, Frederic Barrat wrote:

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)
       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,

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


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).

Alexander, could you please respin your patch to fix the opb_master_regs, too?

I will do it.


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