Re: [PATCH v2 1/8] acpi nvdimm: fix wrong buffer size returned by DSM method

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 12 Aug 2016 14:54:03 +0800
Xiao Guangrong <guangrong.xiao@linux.intel.com> wrote:

> Currently, 'RLEN' is the totally buffer size written by QEMU and it is
> ACPI internally used only. The buffer size returned to guest should
> not include 'RLEN' itself
Do you see any errors in guest with this bug present?
It would be nice to put error messages here so that fix could be found
later just by searching git log and qemu-devel for errors user sees
in guest.


> 
> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> ---
>  hw/acpi/nvdimm.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/hw/acpi/nvdimm.c b/hw/acpi/nvdimm.c
> index e486128..5454c0f 100644
> --- a/hw/acpi/nvdimm.c
> +++ b/hw/acpi/nvdimm.c
> @@ -863,6 +863,8 @@ static void nvdimm_build_common_dsm(Aml *dev)
>  
>      result_size = aml_local(1);
>      aml_append(method, aml_store(aml_name("RLEN"), result_size));
> +    /* RLEN is not included in the payload returned to guest. */
> +    aml_append(method, aml_subtract(result_size, aml_int(4), result_size));
you can merge above store with subtract like this:
  aml_subtract(aml_name("RLEN"), foo, result_size)

Style nit: try not to use magic numbers,
look at how RLEN is defined earlier, extract it into macro and reuse in both places


>      aml_append(method, aml_store(aml_shiftleft(result_size, aml_int(3)),
instead of shiftleft, I'd suggest use here multiply operator and BITS_PER_BYTE
so it would obvious what's going on and rewrite following without intermediate store.

>                                   result_size));
>      aml_append(method, aml_create_field(aml_name("ODAT"), aml_int(0),
aml_create_field(aml_name("ODAT"),
                 aml_int(0),
                 aml_multiply(result_size, aml_int(BITS_PER_BYTE), NULL),
                 "OBUF"))

BTW:
dsm_out_buf_size is more descriptive than result_size

also NCAL later uses Arg6 when method has only 5 arguments which doesn't seem right
instead of arg6 you should make/use local variable 'dsm_out_buf'

As sanity check I'd suggest to extract nvdimm ssdt in guest, decompile and compile it back.
Currently I can't compile it back which mean it's really broken.