Gregory Price wrote:
> The CXL Fixed Memory Window allows for memory aligned down to the
> size of 256MB. However, by default on x86, memory blocks increase
> in size as total System RAM capacity increases. On x86, this caps
> out at 2G when 64GB of System RAM is reached.
>
> When the CFMWS regions are not aligned to memory block size, this
> results in lost capacity on either side of the alignment.
>
> Parse all CFMWS to detect the largest common denomenator among all
> regions, and reduce the block size accordingly.
>
> This can only be done when MEMORY_HOTPLUG and SPARSEMEM configs are
> enabled, but the surrounding code may not necessarily require these
> configs, so build accordingly.
>
> Suggested-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>
> ---
> drivers/acpi/numa/srat.c | 48 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 48 insertions(+)
>
> diff --git a/drivers/acpi/numa/srat.c b/drivers/acpi/numa/srat.c
> index 44f91f2c6c5d..9367d36eba9a 100644
> --- a/drivers/acpi/numa/srat.c
> +++ b/drivers/acpi/numa/srat.c
> @@ -14,6 +14,7 @@
> #include <linux/errno.h>
> #include <linux/acpi.h>
> #include <linux/memblock.h>
> +#include <linux/memory.h>
> #include <linux/numa.h>
> #include <linux/nodemask.h>
> #include <linux/topology.h>
> @@ -333,6 +334,37 @@ acpi_parse_memory_affinity(union acpi_subtable_headers *header,
> return 0;
> }
>
> +#if defined(CONFIG_MEMORY_HOTPLUG)
Generally we avoid config defines in *.c files... See more below.
> +/*
> + * CXL allows CFMW to be aligned along 256MB boundaries, but large memory
> + * systems default to larger alignments (2GB on x86). Misalignments can
> + * cause some capacity to become unreachable. Calculate the largest supported
> + * alignment for all CFMW to maximize the amount of mappable capacity.
> + */
> +static int __init acpi_align_cfmws(union acpi_subtable_headers *header,
> + void *arg, const unsigned long table_end)
> +{
> + struct acpi_cedt_cfmws *cfmws = (struct acpi_cedt_cfmws *)header;
> + u64 start = cfmws->base_hpa;
> + u64 size = cfmws->window_size;
> + unsigned long *fin_bz = arg;
> + unsigned long bz;
> +
> + for (bz = SZ_64T; bz >= SZ_256M; bz >>= 1) {
> + if (IS_ALIGNED(start, bz) && IS_ALIGNED(size, bz))
> + break;
> + }
> +
> + /* Only adjust downward, we never want to increase block size */
> + if (bz < *fin_bz && bz >= SZ_256M)
> + *fin_bz = bz;
> + else if (bz < SZ_256M)
> + pr_err("CFMWS: [BIOS BUG] base/size alignment violates spec\n");
> +
> + return 0;
> +}
> +#endif /* defined(CONFIG_MEMORY_HOTPLUG) */
> +
> static int __init acpi_parse_cfmws(union acpi_subtable_headers *header,
> void *arg, const unsigned long table_end)
> {
> @@ -501,6 +533,10 @@ acpi_table_parse_srat(enum acpi_srat_type id,
> int __init acpi_numa_init(void)
> {
> int i, fake_pxm, cnt = 0;
> +#if defined(CONFIG_MEMORY_HOTPLUG)
> + unsigned long block_sz = memory_block_size_bytes();
To help address David's comment as well;
Is there a way to scan all the alignments of the windows and pass the
desired alignment to the arch in a new call and have the arch determine if
changing the order is ok?
Also the call to the arch would be a noop for !CONFIG_MEMORY_HOTPLUG which
cleans up this function WRT CONFIG_MEMORY_HOTPLUG.
Ira
> + unsigned long cfmw_align = block_sz;
> +#endif /* defined(CONFIG_MEMORY_HOTPLUG) */
>
> if (acpi_disabled)
> return -EINVAL;
> @@ -552,6 +588,18 @@ int __init acpi_numa_init(void)
> }
> last_real_pxm = fake_pxm;
> fake_pxm++;
> +
> +#if defined(CONFIG_MEMORY_HOTPLUG)
> + /* Calculate and set largest supported memory block size alignment */
> + acpi_table_parse_cedt(ACPI_CEDT_TYPE_CFMWS, acpi_align_cfmws,
> + &cfmw_align);
> + if (cfmw_align < block_sz && cfmw_align >= SZ_256M) {
> + if (set_memory_block_size_order(ffs(cfmw_align)-1))
> + pr_warn("CFMWS: Unable to adjust memory block size\n");
> + }
> +#endif /* defined(CONFIG_MEMORY_HOTPLUG) */
> +
> + /* Then parse and fill the numa nodes with the described memory */
> acpi_table_parse_cedt(ACPI_CEDT_TYPE_CFMWS, acpi_parse_cfmws,
> &fake_pxm);
>
> --
> 2.43.0
>
>
