x86/numa: Introduce numa_fill_memblks()

numa_fill_memblks() fills in the gaps in numa_meminfo memblks
over an physical address range.

The ACPI driver will use numa_fill_memblks() to implement a new Linux
policy that prescribes extending proximity domains in a portion of a
CFMWS window to the entire window.

Dan Williams offered this explanation of the policy:
A CFWMS is an ACPI data structure that indicates *potential* locations
where CXL memory can be placed. It is the playground where the CXL
driver has free reign to establish regions. That space can be populated
by BIOS created regions, or driver created regions, after hotplug or
other reconfiguration.

When BIOS creates a region in a CXL Window it additionally describes
that subset of the Window range in the other typical ACPI tables SRAT,
SLIT, and HMAT. The rationale for BIOS not pre-describing the entire
CXL Window in SRAT, SLIT, and HMAT is that it can not predict the
future. I.e. there is nothing stopping higher or lower performance
devices being placed in the same Window. Compare that to ACPI memory
hotplug that just onlines additional capacity in the proximity domain
with little freedom for dynamic performance differentiation.

That leaves the OS with a choice, should unpopulated window capacity
match the proximity domain of an existing region, or should it allocate
a new one? This patch takes the simple position of minimizing proximity
domain proliferation by reusing any proximity domain intersection for
the entire Window. If the Window has no intersections then allocate a
new proximity domain. Note that SRAT, SLIT and HMAT information can be
enumerated dynamically in a standard way from device provided data.
Think of CXL as the end of ACPI needing to describe memory attributes,
CXL offers a standard discovery model for performance attributes, but
Linux still needs to interoperate with the old regime.

Reported-by: Derick Marks <derick.w.marks@intel.com>
Suggested-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: Derick Marks <derick.w.marks@intel.com>
Link: https://lore.kernel.org/all/ef078a6f056ca974e5af85997013c0fda9e3326d.1689018477.git.alison.schofield%40intel.com

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/x86/include/asm/sparsemem.h b/arch/x86/include/asm/sparsemem.h
index 64df897c0ee3..1be13b2dfe8b 100644
--- a/arch/x86/include/asm/sparsemem.h
+++ b/arch/x86/include/asm/sparsemem.h
@@ -37,6 +37,8 @@ extern int phys_to_target_node(phys_addr_t start);
 #define phys_to_target_node phys_to_target_node
 extern int memory_add_physaddr_to_nid(u64 start);
 #define memory_add_physaddr_to_nid memory_add_physaddr_to_nid
+extern int numa_fill_memblks(u64 start, u64 end);
+#define numa_fill_memblks numa_fill_memblks
 #endif
 #endif /* __ASSEMBLY__ */