On Fri, Jun 24, 2016 at 10:44:25AM -0700, Dan Williams wrote:
> QEMU 2.6 implements nascent support for nvdimm DSMs. Depending on
> configuration it may only implement the function0 dsm to indicate that
> no other DSMs are available. Commit 31eca76ba2fc "nfit, libnvdimm:
> limited/whitelisted dimm command marshaling mechanism" breaks QEMU, but
> QEMU is spec compliant. Per the spec the way to indicate that no
> functions are supported is:
>
> If Function Index is zero, the return is a buffer containing one bit
> for each function index, starting with zero. Bit 0 indicates whether
> there is support for any functions other than function 0 for the
> specified UUID and Revision ID. If set to zero, no functions are
> supported (other than function zero) for the specified UUID and
> Revision ID.
Dan,
This breaks calling DSM on HPE platforms and is a regression.
E-mail context can be found at:
https://lists.01.org/pipermail/linux-nvdimm/2016-June/006099.html
The problem with this change is that it assumes that ACPI returning an
object means that the UUID is supported on that platform.
However, looking at ACPI v 6.1 section 9.1.1, the example for
evaluating a _DSM shows that if the UUID is not supported at all,
a zeroed out buffer of length 1 is returned:
//
// If not one of the UUIDs we recognize, then return a buffer
// with bit 0 set to 0 indicating no functions supported.
//
return(Buffer(){0})
HPE firmware has been following this practice for a long long time.
I suspect other manufacturer's firmware do so as well.
The problem is that this creates an ambiguity and the linux code
is no longer differentiating the case where the DSM/UUID is
supported but only implements function 0 (the QEMU case you're
trying to accommodate) and the case that the DSM/UUID is not
supported at all.
The result is that the code in acpi_nfit_add_dimm:
for (i = NVDIMM_FAMILY_INTEL; i <= NVDIMM_FAMILY_HPE2; i++)
- if (acpi_check_dsm(adev_dimm->handle, to_nfit_uuid(i), 1, 1))
+ if (acpi_check_dsm(adev_dimm->handle, to_nfit_uuid(i), 1, 0))
break;
always matches NVDIMM_FAMILY_INTEL. This is either because its
is an Intel nvdimm, or because the unsupported UUID returns back
a zeroed out buffer of length 1.
As nfit_mem->family always equals NVDIMM_FAMILY_INTEL, no subsequent
DSM call will succeed for NVDIMM_FAMILY_HPE1 or any other
family.
I don't have a fix as of yet, but wanted to make you aware of
the problem.
>
> Update the nfit driver to determine the family (interface UUID) without
> requiring the implementation to define any other functions, i.e.
> short-circuit acpi_check_dsm() to succeed per the spec. The nfit driver
> appears to be the only user passing funcs==0 to acpi_check_dsm(), so
> this behavior change of the common routine should be limited to the
> probing done by the nfit driver.
>
> Cc: "Rafael J. Wysocki" <[email protected]>
> Cc: Len Brown <[email protected]>
> Cc: Jerry Hoemann <[email protected]>
> Fixes: 31eca76ba2fc ("nfit, libnvdimm: limited/whitelisted dimm command
> marshaling mechanism")
> Reported-by: Xiao Guangrong <[email protected]>
> Tested-by: Xiao Guangrong <[email protected]>
> Signed-off-by: Dan Williams <[email protected]>
> ---
> drivers/acpi/nfit.c | 6 +++---
> drivers/acpi/utils.c | 6 +++---
> 2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/acpi/nfit.c b/drivers/acpi/nfit.c
> index 2215fc847fa9..32579a7b71d5 100644
> --- a/drivers/acpi/nfit.c
> +++ b/drivers/acpi/nfit.c
> @@ -1131,11 +1131,11 @@ static int acpi_nfit_add_dimm(struct acpi_nfit_desc
> *acpi_desc,
>
> /*
> * Until standardization materializes we need to consider up to 3
> - * different command sets. Note, that checking for function0 (bit0)
> - * tells us if any commands are reachable through this uuid.
> + * different command sets. Note, that checking for zero functions
> + * tells us if any commands might be reachable through this uuid.
> */
> for (i = NVDIMM_FAMILY_INTEL; i <= NVDIMM_FAMILY_HPE2; i++)
> - if (acpi_check_dsm(adev_dimm->handle, to_nfit_uuid(i), 1, 1))
> + if (acpi_check_dsm(adev_dimm->handle, to_nfit_uuid(i), 1, 0))
> break;
At this point i will always == NVDIMM_FAMILY_INTEL.
>
> /* limit the supported commands to those that are publicly documented */
> diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
> index 22c09952e177..b4de130f2d57 100644
> --- a/drivers/acpi/utils.c
> +++ b/drivers/acpi/utils.c
> @@ -680,9 +680,6 @@ bool acpi_check_dsm(acpi_handle handle, const u8 *uuid,
> u64 rev, u64 funcs)
> u64 mask = 0;
> union acpi_object *obj;
>
> - if (funcs == 0)
> - return false;
> -
> obj = acpi_evaluate_dsm(handle, uuid, rev, 0, NULL);
> if (!obj)
> return false;
> @@ -695,6 +692,9 @@ bool acpi_check_dsm(acpi_handle handle, const u8 *uuid,
> u64 rev, u64 funcs)
> mask |= (((u64)obj->buffer.pointer[i]) << (i * 8));
> ACPI_FREE(obj);
Unsupported UUID will get an object. A zeroed out buffer of length 1.
So, acpi_check_dsm is saying supported when it is not.
>
> + if (funcs == 0)
> + return true;
> +
> /*
> * Bit 0 indicates whether there's support for any functions other than
> * function 0 for the specified UUID and revision.
--
-----------------------------------------------------------------------------
Jerry Hoemann Software Engineer Hewlett Packard Enterprise
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