Re: [PATCH] ACPI: NFIT: Fix support for virtual SPA ranges

[Jeff Moyer <jmoyer@redhat.com>]

Dan Williams <dan.j.williams@intel.com> writes:

> Fix the NFIT parsing code to treat a 0 index in a SPA Range Structure as
> a special case and not match Region Mapping Structures that use 0 to
> indicate that they are not mapped. Without this fix some platform BIOS
> descriptions of "virtual disk" ranges do not result in the pmem driver
> attaching to the range.
>
> Details:
> In addition to typical persistent memory ranges, the ACPI NFIT may also
> convey "virtual" ranges. These ranges are indicated by a UUID in the SPA
> Range Structure of UUID_VOLATILE_VIRTUAL_DISK, UUID_VOLATILE_VIRTUAL_CD,
> UUID_PERSISTENT_VIRTUAL_DISK, or UUID_PERSISTENT_VIRTUAL_CD. The
> critical difference between virtual ranges and UUID_PERSISTENT_MEMORY, is
> that virtual do not support associations with Region Mapping Structures.
> For this reason the "index" value of virtual SPA Range Structures is
> allowed to be 0. If a platform BIOS decides to represent unmapped
                                                           ^^^^^^^^
> NVDIMMs with a 0 index in their "SPA Range Structure Index" the driver
  ^^^^^^^

That language confused me.  I thought you were talking about a separate
issue, whereby NVDIMMs which are not mapped (probably due to some errors
with the dimms themselves) would get an index of 0.  But upon
re-reading, I think you just meant that the virtual media is not mapped
via a region mapping structure.

> falsely matches them and may falsely require labels where "virtual
> disks" are expected to be label-less. I.e. label-less is where the
> namespace-range == region-range and the pmem driver attaches with no
> user action to create a namespace.


> Cc: Jacek Zloch <jacek.zloch@intel.com>
> Cc: Lukasz Sobieraj <lukasz.sobieraj@intel.com>
> Cc: "Lee, Chun-Yi" <jlee@suse.com>
> Cc: <stable@vger.kernel.org>
> Fixes: c2f32acdf848 ("acpi, nfit: treat virtual ramdisk SPA as pmem region")
> Reported-by: Krzysztof Rusocki <krzysztof.rusocki@intel.com>
> Reported-by: Damian Bassa <damian.bassa@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/acpi/nfit/core.c |    2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
> index 23d9a09d7060..6f15e56ef955 100644
> --- a/drivers/acpi/nfit/core.c
> +++ b/drivers/acpi/nfit/core.c
> @@ -3021,6 +3021,8 @@ static int acpi_nfit_register_region(struct acpi_nfit_desc *acpi_desc,
>  		struct acpi_nfit_memory_map *memdev = nfit_memdev->memdev;
>  		struct nd_mapping_desc *mapping;
>  
> +		if (memdev->range_index == 0 || spa->range_index == 0)
> +			continue;
>  		if (memdev->range_index != spa->range_index)
>  			continue;
>  		if (count >= ND_MAX_MAPPINGS) {

The change looks good, but can you add a comment to the code?  With
that, you can add my:

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>

Thanks!
Jeff