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[PATCH v3] fw_cfg: Don't set callback_opaque NULL in fw_cfg_modify_bytes


From: Shameer Kolothum
Subject: [PATCH v3] fw_cfg: Don't set callback_opaque NULL in fw_cfg_modify_bytes_read()
Date: Tue, 3 Dec 2024 13:18:06 +0000

On arm/virt platform, Chen Xiang reported a Guest crash while
attempting the below steps,

1. Launch the Guest with nvdimm=on
2. Hot-add a NVDIMM dev
3. Reboot
4. Guest boots fine.
5. Reboot again.
6. Guest boot fails.

QEMU_EFI reports the below error:
ProcessCmdAddPointer: invalid pointer value in "etc/acpi/tables"
OnRootBridgesConnected: InstallAcpiTables: Protocol Error

Debugging shows that on first reboot(after hot adding NVDIMM),
Qemu updates the etc/table-loader len,

qemu_ram_resize()
  fw_cfg_modify_file()
     fw_cfg_modify_bytes_read()

And in fw_cfg_modify_bytes_read() we set the "callback_opaque" for
the key entry to NULL. Because of this, on the second reboot,
virt_acpi_build_update() is called with a NULL "build_state" and
returns without updating the ACPI tables. This seems to be
upsetting the firmware.

To fix this, don't change the callback_opaque in fw_cfg_modify_bytes_read().

Fixes: bdbb5b1706d165 ("fw_cfg: add fw_cfg_machine_reset function")
Reported-by: chenxiang <chenxiang66@hisilicon.com>
Acked-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
---
Hi,

I forgot to follow-up on the v2 and it never got picked up.
Thanks to Wangzhou who recently re-run the tests and found that
the problem mentioned above still exists. Hence resending the v2.

v2-->v3:
 -Just rebase.

v2: 
https://lore.kernel.org/qemu-devel/20220908160354.2023-1-shameerali.kolothum.thodi@huawei.com/
v1: 
https://lore.kernel.org/all/20220825161842.841-1-shameerali.kolothum.thodi@huawei.com/

Thanks,
Shameer
---
 hw/nvram/fw_cfg.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index b644577734..74edb1e4cf 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -730,7 +730,6 @@ static void *fw_cfg_modify_bytes_read(FWCfgState *s, 
uint16_t key,
     ptr = s->entries[arch][key].data;
     s->entries[arch][key].data = data;
     s->entries[arch][key].len = len;
-    s->entries[arch][key].callback_opaque = NULL;
     s->entries[arch][key].allow_write = false;
 
     return ptr;
-- 
2.34.1




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