x86: probe memory block size advisement value during mm init

Systems with hotplug may provide an advisement value on what the memblock
size should be.  Probe this value when the rest of the configuration
values are considered.

The new heuristic is as follows

1) set_memory_block_size_order value if already set (cmdline param)
2) minimum block size if memory is less than large block limit
3) if no hotplug advice: Max block size if system is bare-metal,
   otherwise use end of memory alignment.
4) if hotplug advice: lesser of advice and end of memory alignment.

Convert to cpu_feature_enabled() while at it.[1]

[1] https://lore.kernel.org/all/20241031103401.GBZyNdGQ-ZyXKyzC_z@fat_crate.local/

Link: https://lkml.kernel.org/r/20250127153405.3379117-3-gourry@gourry.net
Signed-off-by: Gregory Price <gourry@gourry.net>
Suggested-by: Borislav Petkov <bp@alien8.de>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: Fan Ni <fan.ni@samsung.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Bruno Faccini <bfaccini@nvidia.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Haibo Xu <haibo1.xu@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joanthan Cameron <Jonathan.Cameron@huawei.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Robert Richter <rrichter@amd.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 7c4f6f591f2b244dbc1173822b7230e2024cab23..8cea7dcf8fa015712895aa727cba26606969af9b 100644 (file)
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1464,16 +1464,21 @@ static unsigned long probe_memory_block_size(void)
        }
 
        /*
-        * Use max block size to minimize overhead on bare metal, where
-        * alignment for memory hotplug isn't a concern.
+        * When hotplug alignment is not a concern, maximize blocksize
+        * to minimize overhead. Otherwise, align to the lesser of advice
+        * alignment and end of memory alignment.
         */
-       if (!boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
+       bz = memory_block_advised_max_size();
+       if (!bz) {
                bz = MAX_BLOCK_SIZE;
-               goto done;
+               if (!cpu_feature_enabled(X86_FEATURE_HYPERVISOR))
+                       goto done;
+       } else {
+               bz = max(min(bz, MAX_BLOCK_SIZE), MIN_MEMORY_BLOCK_SIZE);
        }
 
        /* Find the largest allowed block size that aligns to memory end */
-       for (bz = MAX_BLOCK_SIZE; bz > MIN_MEMORY_BLOCK_SIZE; bz >>= 1) {
+       for (; bz > MIN_MEMORY_BLOCK_SIZE; bz >>= 1) {
                if (IS_ALIGNED(boot_mem_end, bz))
                        break;
        }