Re: [PATCH] fw_cfg: Don't set callback_opaque NULL in fw_cfg_modify_bytes_read()

[Laszlo Ersek <lersek@redhat.com>]

On 08/25/22 18:18, Shameer Kolothum wrote:
> Hi
> 
> 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().
> 
> Reported-by: chenxiang <chenxiang66@hisilicon.com>
> Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> ---
> I am still not very convinced this is the root cause of the issue.
> Though it looks like setting callback_opaque to NULL while updating
> the file size is wrong, what puzzles me is that on the second reboot
> we don't have any ACPI table size changes and ideally firmware should
> see the updated tables from the first reboot itself.
> 
> Please take a look and let me know.
> 
> 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 d605f3f45a..dfe8404c01 100644
> --- a/hw/nvram/fw_cfg.c
> +++ b/hw/nvram/fw_cfg.c
> @@ -728,7 +728,6 @@ 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;
> 

I vaguely recall seeing the same issue report years ago (also in
relation to hot-adding NVDIMM). However, I have no capacity to
participate in the discussion. Making this remark just for clarity.

Laszlo