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

From: Jerry Hoemann <jerry.hoemann@hpe.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>
Subject: Re: [PATCH v4 3/6] libnvdimm, acpi, nfit: Add bus level dsm mask for pass thru.
Date: Tue, 4 Jul 2017 14:08:49 -0600	[thread overview]
Message-ID: <20170704200849.GA15713@anatevka.americas.hpqcorp.net> (raw)
In-Reply-To: <CAPcyv4iMNjea939-E8of0nuyze8nHMEOp3ecii8+Y3pyYE0Ecw@mail.gmail.com>

On Sat, Jul 01, 2017 at 01:46:03PM -0700, Dan Williams wrote:
> On Sat, Jul 1, 2017 at 1:38 PM, Jerry Hoemann <jerry.hoemann@hpe.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@intel.com> wrote:
> >> > On Sat, Jul 1, 2017 at 12:58 PM, Jerry Hoemann <jerry.hoemann@hpe.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@hpe.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

No.  It is not needless.  It is not an ABI extension.
Same goes for the override feature.

I hope that ACPI doesn't extend the specification in the future because
we'll just have to redo these patches yet again.

-- 

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Jerry Hoemann                  Software Engineer   Hewlett Packard Enterprise
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