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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: Thu, 11 May 2023 11:36:58 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0

On 5/11/23 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?

There are other processors:

powernv10            IBM PowerNV (Non-Virtualized) POWER10
powernv8             IBM PowerNV (Non-Virtualized) POWER8
powernv              IBM PowerNV (Non-Virtualized) POWER9 (alias of powernv9)
powernv9             IBM PowerNV (Non-Virtualized) POWER9

Region lpc->opb_master_regs needs to be tagged also for powernv9 and



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

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