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

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Message-ID: <CAPcyv4hP0zuZ0bdcQ5R3K2p5CRfHKXMSC_ov1D4qGXsXAQen=A@mail.gmail.com>
Date:   Sat, 1 Jul 2017 13:10:31 -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 1:08 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.

Actually, just the discovery portion does not lead to this leak, but
it's redundant when we have the 'dsm_mask' sysfs attribute.