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

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 17 Jan 2020 17:45:17 +0000
Shameer Kolothum <shameerali.kolothum.thodi@huawei.com> 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 <imammedo@redhat.com>
> Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> ---
> 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

> +    offset = aml_local(2);
> +    aml_append(ifctx, aml_store(aml_int(0), offset));
> +    aml_append(ifctx, aml_name_decl("TBUF", aml_buffer(1, NULL)));
> +    aml_append(ifctx, aml_store(aml_buffer(0, NULL), dsm_out_buf));
> +
> +    whilectx = aml_while(aml_lless(offset, dsm_out_buf_size));
> +    /* Copy 1 byte at offset from ODAT to temporary buffer(TBUF). */
> +    aml_append(whilectx, aml_store(aml_derefof(aml_index(
> +                                   aml_name(NVDIMM_DSM_OUT_BUF), offset)),
> +                                   aml_index(aml_name("TBUF"), aml_int(0))));
> +    aml_append(whilectx, aml_concatenate(dsm_out_buf, aml_name("TBUF"),
> +                                         dsm_out_buf));
> +    aml_append(whilectx, aml_increment(offset));
> +    aml_append(ifctx, whilectx);
> +
> +    aml_append(ifctx, aml_return(dsm_out_buf));
> +    aml_append(method, ifctx);
> +
> +    /* If RLEN >= Integer size, just use CreateField() operator */
>      aml_append(method, aml_store(aml_shiftleft(dsm_out_buf_size, aml_int(3)),
>                                   dsm_out_buf_size));
>      aml_append(method, aml_create_field(aml_name(NVDIMM_DSM_OUT_BUF),
>                 aml_int(0), dsm_out_buf_size, "OBUF"));
> -    aml_append(method, aml_concatenate(aml_buffer(0, NULL), aml_name("OBUF"),
> -                                       dsm_out_buf));
> -    aml_append(method, aml_return(dsm_out_buf));
> +    aml_append(method, aml_return(aml_name("OBUF")));
> +
>      aml_append(dev, method);
>  }
>  
> diff --git a/tests/qtest/bios-tables-test-allowed-diff.h b/tests/qtest/bios-tables-test-allowed-diff.h
> index dfb8523c8b..eb8bae1407 100644
> --- a/tests/qtest/bios-tables-test-allowed-diff.h
> +++ b/tests/qtest/bios-tables-test-allowed-diff.h
> @@ -1 +1,3 @@
>  /* List of comma-separated changed AML files to ignore */
> +"tests/data/acpi/pc/SSDT.dimmpxm",
> +"tests/data/acpi/q35/SSDT.dimmpxm",