linux-kernel - Re: [PATCH v2 6/6] ACPI: HMAT: Attach a device for each soft-reserved range

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Date:   Tue, 24 Mar 2020 14:06:52 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Joao Martins <joao.m.martins@...cle.com>
Cc:     Linux ACPI <linux-acpi@...r.kernel.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Brice Goglin <Brice.Goglin@...ia.fr>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>
Subject: Re: [PATCH v2 6/6] ACPI: HMAT: Attach a device for each soft-reserved range

On Tue, Mar 24, 2020 at 12:41 PM Joao Martins <joao.m.martins@...cle.com> wrote:
>
> On 3/22/20 4:12 PM, Dan Williams wrote:
> > The hmem enabling in commit 'cf8741ac57ed ("ACPI: NUMA: HMAT: Register
> > "soft reserved" memory as an "hmem" device")' only registered ranges to
> > the hmem driver for each soft-reservation that also appeared in the
> > HMAT. While this is meant to encourage platform firmware to "do the
> > right thing" and publish an HMAT, the corollary is that platforms that
> > fail to publish an accurate HMAT will strand memory from Linux usage.
> > Additionally, the "efi_fake_mem" kernel command line option enabling
> > will strand memory by default without an HMAT.
> >
> > Arrange for "soft reserved" memory that goes unclaimed by HMAT entries
> > to be published as raw resource ranges for the hmem driver to consume.
> >
> > Include a module parameter to disable either this fallback behavior, or
> > the hmat enabling from creating hmem devices. The module parameter
> > requires the hmem device enabling to have unique name in the module
> > namespace: "device_hmem".
> >
> > Rather than mark this x86-only, include an interim phys_to_target_node()
> > implementation for arm64.
> >
> > Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> > Cc: Brice Goglin <Brice.Goglin@...ia.fr>
> > Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> > Cc: Jeff Moyer <jmoyer@...hat.com>
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: Will Deacon <will@...nel.org>
> > Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> > ---
> >  arch/arm64/mm/numa.c      |   13 +++++++++++++
> >  drivers/dax/Kconfig       |    1 +
> >  drivers/dax/hmem/Makefile |    3 ++-
> >  drivers/dax/hmem/device.c |   33 +++++++++++++++++++++++++++++++++
> >  4 files changed, 49 insertions(+), 1 deletion(-)
> >
>
> [...]
>
> > diff --git a/drivers/dax/hmem/device.c b/drivers/dax/hmem/device.c
> > index 99bc15a8b031..f9c5fa8b1880 100644
> > --- a/drivers/dax/hmem/device.c
> > +++ b/drivers/dax/hmem/device.c
> > @@ -4,6 +4,9 @@
> >  #include <linux/module.h>
> >  #include <linux/mm.h>
> >
> > +static bool nohmem;
> > +module_param_named(disable, nohmem, bool, 0444);
> > +
> >  void hmem_register_device(int target_nid, struct resource *r)
> >  {
> >       /* define a clean / non-busy resource for the platform device */
> > @@ -16,6 +19,9 @@ void hmem_register_device(int target_nid, struct resource *r)
> >       struct memregion_info info;
> >       int rc, id;
> >
> > +     if (nohmem)
> > +             return;
> > +
> >       rc = region_intersects(res.start, resource_size(&res), IORESOURCE_MEM,
> >                       IORES_DESC_SOFT_RESERVED);
> >       if (rc != REGION_INTERSECTS)
> > @@ -62,3 +68,30 @@ void hmem_register_device(int target_nid, struct resource *r)
> >  out_pdev:
> >       memregion_free(id);
> >  }
> > +
> > +static __init int hmem_register_one(struct resource *res, void *data)
> > +{
> > +     /*
> > +      * If the resource is not a top-level resource it was already
> > +      * assigned to a device by the HMAT parsing.
> > +      */
> > +     if (res->parent != &iomem_resource)
> > +             return 0;
> > +
> > +     hmem_register_device(phys_to_target_node(res->start), res);
> > +
> > +     return 0;
>
> Should we add an error returning value to hmem_register_device() perhaps this
> ought to be reflected in hmem_register_one().
>
> > +}
> > +
> > +static __init int hmem_init(void)
> > +{
> > +     walk_iomem_res_desc(IORES_DESC_SOFT_RESERVED,
> > +                     IORESOURCE_MEM, 0, -1, NULL, hmem_register_one);
> > +     return 0;
> > +}
> > +
>
> (...) and then perhaps here returning in the initcall if any of the resources
> failed hmem registration?

Except that hmem_register_one() is a stop-gap to collect soft-reserved
ranges that were not already registered, and it's not an error to find
already registered devices. However, I do think it's a good idea to
log registrations that failed for other reasons.