linux-kernel - Re: [PATCHv2 02/12] acpi/hmat: Parse and report heterogeneous memory

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Date:   Mon, 10 Dec 2018 22:03:40 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Keith Busch <keith.busch@...el.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCHv2 02/12] acpi/hmat: Parse and report heterogeneous memory

On Mon, Dec 10, 2018 at 5:05 PM Keith Busch <keith.busch@...el.com> wrote:
>
> Systems may provide different memory types and export this information
> in the ACPI Heterogeneous Memory Attribute Table (HMAT). Parse these
> tables provided by the platform and report the memory access and caching
> attributes.
>
> Signed-off-by: Keith Busch <keith.busch@...el.com>
> ---
>  drivers/acpi/Kconfig  |   8 +++
>  drivers/acpi/Makefile |   1 +
>  drivers/acpi/hmat.c   | 192 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  drivers/acpi/tables.c |   9 +++
>  include/linux/acpi.h  |   1 +
>  5 files changed, 211 insertions(+)
>  create mode 100644 drivers/acpi/hmat.c
>
> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> index 7cea769c37df..9a05af3a18cf 100644
> --- a/drivers/acpi/Kconfig
> +++ b/drivers/acpi/Kconfig
> @@ -327,6 +327,14 @@ config ACPI_NUMA
>         depends on (X86 || IA64 || ARM64)
>         default y if IA64_GENERIC || IA64_SGI_SN2 || ARM64
>
> +config ACPI_HMAT
> +       bool "ACPI Heterogeneous Memory Attribute Table Support"
> +       depends on ACPI_NUMA
> +       help
> +        Parses representation of the ACPI Heterogeneous Memory Attributes
> +        Table (HMAT) and set the memory node relationships and access
> +        attributes.
> +
>  config ACPI_CUSTOM_DSDT_FILE
>         string "Custom DSDT Table file to include"
>         default ""
> diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
> index edc039313cd6..b5e13499f88b 100644
> --- a/drivers/acpi/Makefile
> +++ b/drivers/acpi/Makefile
> @@ -55,6 +55,7 @@ acpi-$(CONFIG_X86)            += x86/apple.o
>  acpi-$(CONFIG_X86)             += x86/utils.o
>  acpi-$(CONFIG_DEBUG_FS)                += debugfs.o
>  acpi-$(CONFIG_ACPI_NUMA)       += numa.o
> +acpi-$(CONFIG_ACPI_HMAT)       += hmat.o
>  acpi-$(CONFIG_ACPI_PROCFS_POWER) += cm_sbs.o
>  acpi-y                         += acpi_lpat.o
>  acpi-$(CONFIG_ACPI_LPIT)       += acpi_lpit.o
> diff --git a/drivers/acpi/hmat.c b/drivers/acpi/hmat.c
> new file mode 100644
> index 000000000000..ef3881f0f370
> --- /dev/null
> +++ b/drivers/acpi/hmat.c
[..]
> +static __init int hmat_init(void)
> +{
> +       struct acpi_subtable_proc subtable_proc;
> +       struct acpi_table_header *tbl;
> +       enum acpi_hmat_type i;
> +       acpi_status status;
> +
> +       if (srat_disabled())
> +               return 0;
> +
> +       status = acpi_get_table(ACPI_SIG_HMAT, 0, &tbl);
> +       if (ACPI_FAILURE(status))
> +               return 0;
> +
> +       if (acpi_table_parse(ACPI_SIG_HMAT, parse_noop))
> +               goto out_put;
> +
> +       memset(&subtable_proc, 0, sizeof(subtable_proc));
> +       subtable_proc.handler = hmat_parse_subtable;
> +       for (i = ACPI_HMAT_TYPE_ADDRESS_RANGE; i < ACPI_HMAT_TYPE_RESERVED; i++) {
> +               subtable_proc.id = i;
> +               if (acpi_table_parse_entries_array(ACPI_SIG_HMAT,
> +                                       sizeof(struct acpi_table_hmat),
> +                                       &subtable_proc, 1, 0) < 0)
> +                       goto out_put;
> +       }
> + out_put:
> +       acpi_put_table(tbl);
> +       return 0;
> +}
> +subsys_initcall(hmat_init);

I have a use case to detect the presence of a memory-side-cache early
at init time [1]. To me this means that hmat_init() needs to happen as
a part of acpi_numa_init(). Subsequently I think that also means that
the sysfs portion needs to be broken out to its own init path that can
probably run at module_init() priority.

Perhaps we should split this patch set into two? The table parsing
with an in-kernel user is a bit easier to reason about and can go in
first. Towards that end can I steal / refllow patches 1 & 2 into the
memory randomization series? Other ideas how to handle this?

[1]: https://lkml.org/lkml/2018/10/12/309