RE: [PATCH v2 2/7] hw/acpi/nvdimm: Fix for NVDIMM incorrect DSM output buffer length

[Shameerali Kolothum Thodi]

> -----Original Message-----
> From: Igor Mammedov [mailto:address@hidden]
> Sent: 06 February 2020 16:06
> To: Shameerali Kolothum Thodi <address@hidden>
> Cc: address@hidden; address@hidden;
> address@hidden; address@hidden;
> address@hidden; address@hidden; Linuxarm
> <address@hidden>; xuwei (O) <address@hidden>;
> address@hidden; address@hidden
> Subject: Re: [PATCH v2 2/7] hw/acpi/nvdimm: Fix for NVDIMM incorrect DSM
> output buffer length
> 
> On Fri, 17 Jan 2020 17:45:17 +0000
> Shameer Kolothum <address@hidden> wrote:
> 
> > As per ACPI spec 6.3, Table 19-419 Object Conversion Rules, if the
> > Buffer Field <= to the size of an Integer (in bits), it will be
> > treated as an integer. Moreover, the integer size depends on DSDT
> > tables revision number. If revision number is < 2, integer size is 32
> > bits, otherwise it is 64 bits. Current NVDIMM common DSM aml code
> > (NCAL) uses CreateField() for creating DSM output buffer. This creates
> > an issue in arm/virt platform where DSDT revision number is 2 and
> > results in DSM buffer with a wrong
> > size(8 bytes) gets returned when actual length is < 8 bytes.
> > This causes guest kernel to report,
> >
> > "nfit ACPI0012:00: found a zero length table '0' parsing nfit"
> >
> > In order to fix this, aml code is now modified such that it builds the
> > DSM output buffer in a byte by byte fashion when length is smaller
> > than Integer size.
> >
> > Suggested-by: Igor Mammedov <address@hidden>
> > Signed-off-by: Shameer Kolothum <address@hidden>
> > ---
> > Please find the previous discussion on this here,
> > https://patchwork.kernel.org/cover/11174959/
> >
> > ---
> >  hw/acpi/nvdimm.c                            | 36
> +++++++++++++++++++--
> >  tests/qtest/bios-tables-test-allowed-diff.h |  2 ++
> >  2 files changed, 35 insertions(+), 3 deletions(-)
> >
> > diff --git a/hw/acpi/nvdimm.c b/hw/acpi/nvdimm.c index
> > 9fdad6dc3f..5e7b8318d0 100644
> > --- a/hw/acpi/nvdimm.c
> > +++ b/hw/acpi/nvdimm.c
> > @@ -964,6 +964,7 @@ static void nvdimm_build_common_dsm(Aml *dev)
> >      Aml *method, *ifctx, *function, *handle, *uuid, *dsm_mem,
> *elsectx2;
> >      Aml *elsectx, *unsupport, *unpatched, *expected_uuid, *uuid_invalid;
> >      Aml *pckg, *pckg_index, *pckg_buf, *field, *dsm_out_buf,
> > *dsm_out_buf_size;
> > +    Aml *whilectx, *offset;
> >      uint8_t byte_list[1];
> >
> >      method = aml_method(NVDIMM_COMMON_DSM, 5,
> AML_SERIALIZED); @@
> > -1117,13 +1118,42 @@ static void nvdimm_build_common_dsm(Aml *dev)
> >      /* RLEN is not included in the payload returned to guest. */
> >      aml_append(method,
> aml_subtract(aml_name(NVDIMM_DSM_OUT_BUF_SIZE),
> >                 aml_int(4), dsm_out_buf_size));
> > +
> > +    /*
> > +     * As per ACPI spec 6.3, Table 19-419 Object Conversion Rules, if
> > +     * the Buffer Field <= to the size of an Integer (in bits), it will
> > +     * be treated as an integer. Moreover, the integer size depends on
> > +     * DSDT tables revision number. If revision number is < 2, integer
> > +     * size is 32 bits, otherwise it is 64 bits.
> > +     * Because of this CreateField() canot be used if RLEN < Integer Size.
> > +     * Hence build dsm_out_buf byte by byte.
> > +     */
> > +    ifctx = aml_if(aml_lless(dsm_out_buf_size,
> > + aml_sizeof(aml_int(0))));
> 
> this decomplies into
> 
>  If (Local1 < SizeOf ())
> 
> which doesn't look right

Ok. I tried printing the value returned(SizeOf) and that looks alright.

Anyway, changed it into aml_int(1) which decompiles to

   If (Local1 < SizeOf (One))

Hope this is acceptable.

Thanks,
Shameer