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" <rjw@xxxxxxxxxxxxx> > Cc: Len Brown <lenb@xxxxxxxxxx> > Cc: Jerry Hoemann <jerry.hoemann@xxxxxxx> > Fixes: 31eca76ba2fc ("nfit, libnvdimm: limited/whitelisted dimm command marshaling mechanism") > Reported-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx> > Tested-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx> > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> > --- > 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 ----------------------------------------------------------------------------- -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
