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

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Message-ID: <ecfd5f74-cc03-5590-82df-6f7a3dbcdb50@oracle.com>
Date:   Tue, 24 Mar 2020 21:30:42 +0000
From:   Joao Martins <joao.m.martins@...cle.com>
To:     Dan Williams <dan.j.williams@...el.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 3/24/20 9:06 PM, Dan Williams wrote:
> 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. 
> 
/nods

And if we were to return an error (say for hmem0 out of 4 hmem ones)  before
walking through all soft-reserved found resources, if would skip registration
for the remaining ones.

  Joao