x86/clear_page: introduce clear_pages()

Performance when clearing with string instructions (x86-64-stosq and
similar) can vary significantly based on the chunk-size used.

  $ perf bench mem memset -k 4KB -s 4GB -f x86-64-stosq
  # Running 'mem/memset' benchmark:
  # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
  # Copying 4GB bytes ...

      13.748208 GB/sec

  $ perf bench mem memset -k 2MB -s 4GB -f x86-64-stosq
  # Running 'mem/memset' benchmark:
  # function 'x86-64-stosq' (movsq-based memset() in
  # arch/x86/lib/memset_64.S)
  # Copying 4GB bytes ...

      15.067900 GB/sec

  $ perf bench mem memset -k 1GB -s 4GB -f x86-64-stosq
  # Running 'mem/memset' benchmark:
  # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
  # Copying 4GB bytes ...

      38.104311 GB/sec

(Both on AMD Milan.)

With a change in chunk-size from 4KB to 1GB, we see the performance go
from 13.7 GB/sec to 38.1 GB/sec.  For the chunk-size of 2MB the change
isn't quite as drastic but it is worth adding a clear_page() variant that
can handle contiguous page-extents.

Link: https://lkml.kernel.org/r/20260107072009.1615991-6-ankur.a.arora@oracle.com
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Tested-by: Raghavendra K T <raghavendra.kt@amd.com>
Reviewed-by: David Hildenbrand (Red Hat) <david@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Konrad Rzessutek Wilk <konrad.wilk@oracle.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Li Zhe <lizhe.67@bytedance.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 12 insertions, 5 deletions

diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index ec3307234a17..1895c207f629 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -52,8 +52,9 @@ void __clear_pages_unrolled(void *page);
 KCFI_REFERENCE(__clear_pages_unrolled);
 
 /**
- * clear_page() - clear a page using a kernel virtual address.
- * @addr: address of kernel page
+ * clear_pages() - clear a page range using a kernel virtual address.
+ * @addr: start address of kernel page range
+ * @npages: number of pages
  *
  * Switch between three implementations of page clearing based on CPU
  * capabilities:
@@ -81,11 +82,11 @@ KCFI_REFERENCE(__clear_pages_unrolled);
  *
  * Does absolutely no exception handling.
  */
-static inline void clear_page(void *addr)
+static inline void clear_pages(void *addr, unsigned int npages)
 {
-	u64 len = PAGE_SIZE;
+	u64 len = npages * PAGE_SIZE;
 	/*
-	 * Clean up KMSAN metadata for the page being cleared. The assembly call
+	 * Clean up KMSAN metadata for the pages being cleared. The assembly call
 	 * below clobbers @addr, so perform unpoisoning before it.
 	 */
 	kmsan_unpoison_memory(addr, len);
@@ -106,6 +107,12 @@ static inline void clear_page(void *addr)
 			: "a" (0)
 			: "cc", "memory");
 }
+#define clear_pages clear_pages
+
+static inline void clear_page(void *addr)
+{
+	clear_pages(addr, 1);
+}
 
 void copy_page(void *to, void *from);
 KCFI_REFERENCE(copy_page);