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

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Date:   Wed, 25 Mar 2020 11:10:40 +0000
From:   Will Deacon <will@...nel.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     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>,
        Jeff Moyer <jmoyer@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        peterz@...radead.org, dave.hansen@...ux.intel.com,
        linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, joao.m.martins@...cle.com
Subject: Re: [PATCH v2 6/6] ACPI: HMAT: Attach a device for each
 soft-reserved range

On Sun, Mar 22, 2020 at 09:12:58AM -0700, 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/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
> index 4decf1659700..00fba21eaec0 100644
> --- a/arch/arm64/mm/numa.c
> +++ b/arch/arm64/mm/numa.c
> @@ -468,3 +468,16 @@ int memory_add_physaddr_to_nid(u64 addr)
>  	pr_warn("Unknown node for memory at 0x%llx, assuming node 0\n", addr);
>  	return 0;
>  }
> +
> +/*
> + * device-dax instance registrations want a valid target-node in case
> + * they are ever onlined as memory (see hmem_register_device()).
> + *
> + * TODO: consult cached numa info
> + */
> +int phys_to_target_node(phys_addr_t addr)
> +{
> +	pr_warn_once("Unknown target node for memory at 0x%llx, assuming node 0\n",
> +			addr);
> +	return 0;
> +}

Could you implement a generic version of this by iterating over the nodes
with for_each_{,online_}node() and checking for intersection with
node_{start,end}_pfn()?

Will