linux-kernel - Re: [PATCH v4 3/6] libnvdimm, acpi, nfit: Add bus level dsm mask for pass thru.

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Date:   Sat, 1 Jul 2017 13:46:03 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jerry Hoemann <Jerry.Hoemann@....com>
Cc:     "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/6] libnvdimm, acpi, nfit: Add bus level dsm mask for
 pass thru.

On Sat, Jul 1, 2017 at 1:38 PM, Jerry Hoemann <jerry.hoemann@....com> wrote:
> On Sat, Jul 01, 2017 at 01:10:31PM -0700, Dan Williams wrote:
>> On Sat, Jul 1, 2017 at 1:08 PM, Dan Williams <dan.j.williams@...el.com> wrote:
>> > On Sat, Jul 1, 2017 at 12:58 PM, Jerry Hoemann <jerry.hoemann@....com> wrote:
>> >> On Fri, Jun 30, 2017 at 08:55:22PM -0700, Dan Williams wrote:
>> >>
>> >> ...
>> >>
>> >>> On Fri, Jun 30, 2017 at 9:09 AM, Jerry Hoemann <jerry.hoemann@....com> wrote:
>> >>> > +               if (cmd == ND_CMD_CALL)
>> >>> > +                       dsm_mask = nd_desc->bus_dsm_mask;
>> >>> >                 desc = nd_cmd_bus_desc(cmd);
>> >>> >                 uuid = to_nfit_uuid(NFIT_DEV_BUS);
>> >>> >                 handle = adev->handle;
>> >>> > @@ -1613,6 +1615,7 @@ static void acpi_nfit_init_dsms(struct acpi_nfit_desc *acpi_desc)
>> >>> >         struct nvdimm_bus_descriptor *nd_desc = &acpi_desc->nd_desc;
>> >>> >         const u8 *uuid = to_nfit_uuid(NFIT_DEV_BUS);
>> >>> >         struct acpi_device *adev;
>> >>> > +       unsigned long dsm_mask;
>> >>> >         int i;
>> >>> >
>> >>> >         nd_desc->cmd_mask = acpi_desc->bus_cmd_force_en;
>> >>> > @@ -1624,6 +1627,11 @@ static void acpi_nfit_init_dsms(struct acpi_nfit_desc *acpi_desc)
>> >>> >                 if (acpi_check_dsm(adev->handle, uuid, 1, 1ULL << i))
>> >>> >                         set_bit(i, &nd_desc->cmd_mask);
>> >>> >         set_bit(ND_CMD_CALL, &nd_desc->cmd_mask);
>> >>> > +
>> >>> > +       dsm_mask = 0x3bf;
>> >>>
>> >>> I went ahead and fixed this up to use dsm_mask defined like this:
>> >>>
>> >>> +       dsm_mask =
>> >>> +               (1 << ND_CMD_ARS_CAP) |
>> >>> +               (1 << ND_CMD_ARS_START) |
>> >>> +               (1 << ND_CMD_ARS_STATUS) |
>> >>> +               (1 << ND_CMD_CLEAR_ERROR) |
>> >>> +               (1 << NFIT_CMD_TRANSLATE_SPA) |
>> >>> +               (1 << NFIT_CMD_ARS_INJECT_SET) |
>> >>> +               (1 << NFIT_CMD_ARS_INJECT_CLEAR) |
>> >>> +               (1 << NFIT_CMD_ARS_INJECT_GET);
>> >>>
>> >>> This drops function number 0 which userspace has no need to call.
>> >>
>> >> Actually I like to call function 0.  Its an excellent test when
>> >> modifying the code path as its a no side effects function whose output
>> >> is known in advance and instantly recognizable.  I also use it when
>> >> testing new firmware.
>> >>
>> >> What is the downside to allowing it?  What bad things happen?
>> >
>> > It allows implementations to bypass the standardization process and
>> > ship new root DSMs. It's always possible to patch the kernel locally
>> > for development, so I see no reason to ship this capability globally.
>
> I don't understand this comment, but I think your next comment
> essentially says to disregard this comment?

Yes, sorry.

>> Actually, just the discovery portion does not lead to this leak, but
>> it's redundant when we have the 'dsm_mask' sysfs attribute.
>
> No.  The generation of the mask in sysfs is not done by
> executing the code in acpi_nfit_ctl.  One of the reasons I call
> function 0 to test changes I am making to the ioctl path itself.
> The sysfs has nothing to do with that path and cannot be used
> to serve this purpose.
>
> And since the content of sysfs has been edited it also can not be
> used as a basic test of firmware.
>
> What is the downside to allowing the calling of function 0?

It needlessly expands the kernel ABI. I would suggest, if you want to
test acpi_nfit_ctl() path changes, expand the existing test
infrastructure we have in nfit_ctl_test(). If you want to test
firmware you don't need the upstream kernel to carry firmware debug
enabling in the production path, but I would support expanding
tools/testing/nvdimm/ to make it easier to test firmware.