linux-kernel - [PATCH 4/9] x86/clear_page: parameterize clear

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Date:   Sun,  2 Apr 2023 22:22:28 -0700
From:   Ankur Arora <ankur.a.arora@...cle.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Cc:     torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
        luto@...nel.org, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, mingo@...hat.com, juri.lelli@...hat.com,
        willy@...radead.org, mgorman@...e.de, peterz@...radead.org,
        rostedt@...dmis.org, tglx@...utronix.de,
        vincent.guittot@...aro.org, jon.grimm@....com, bharata@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        ankur.a.arora@...cle.com
Subject: [PATCH 4/9] x86/clear_page: parameterize clear_page*() to specify length

Change clear_page*() to take a length parameter.
Rename to clear_pages_*().

Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---

clear_page() is now defined in terms of clear_pages(). This means
that all clear_page() callsites -- which are more numerous -- would
use an additional register now.

Opinions on if that's worth optimizing?

---
 arch/x86/include/asm/page_64.h | 18 ++++++++------
 arch/x86/lib/clear_page_64.S   | 45 +++++++++++++++++++++++++---------
 2 files changed, 43 insertions(+), 20 deletions(-)

diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index cc6b8e087192..7ca3bd2448c1 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -39,22 +39,24 @@ extern unsigned long __phys_addr_symbol(unsigned long);
 
 #define __phys_reloc_hide(x)	(x)
 
-void clear_page_orig(void *page);
-void clear_page_rep(void *page);
-void clear_page_erms(void *page);
+void clear_pages_orig(void *page, unsigned int length);
+void clear_pages_rep(void *page, unsigned int length);
+void clear_pages_erms(void *page, unsigned int length);
 
 static inline void clear_page(void *page)
 {
+	unsigned long length = PAGE_SIZE;
 	/*
 	 * Clean up KMSAN metadata for the page being cleared. The assembly call
 	 * below clobbers @page, so we perform unpoisoning before it.
 	 */
-	kmsan_unpoison_memory(page, PAGE_SIZE);
-	alternative_call_2(clear_page_orig,
-			   clear_page_rep, X86_FEATURE_REP_GOOD,
-			   clear_page_erms, X86_FEATURE_ERMS,
+	kmsan_unpoison_memory(page, length);
+
+	alternative_call_2(clear_pages_orig,
+			   clear_pages_rep, X86_FEATURE_REP_GOOD,
+			   clear_pages_erms, X86_FEATURE_ERMS,
 			   "=D" (page),
-			   "0" (page)
+			   "0" (page), "S" (length)
 			   : "cc", "memory", "rax", "rcx");
 }
 
diff --git a/arch/x86/lib/clear_page_64.S b/arch/x86/lib/clear_page_64.S
index ecbfb4dd3b01..6069acf6072f 100644
--- a/arch/x86/lib/clear_page_64.S
+++ b/arch/x86/lib/clear_page_64.S
@@ -2,6 +2,8 @@
 #include <linux/linkage.h>
 #include <asm/asm.h>
 #include <asm/export.h>
+#include <asm/cpufeatures.h>
+#include <asm/alternative.h>
 
 /*
  * Most CPUs support enhanced REP MOVSB/STOSB instructions. It is
@@ -13,18 +15,30 @@
 /*
  * Zero a page.
  * %rdi	- page
+ * %esi	- page-length
+ *
+ * Clobbers: %rax, %rcx
  */
-SYM_FUNC_START(clear_page_rep)
-	movl $4096/8,%ecx
+SYM_FUNC_START(clear_pages_rep)
+	movl %esi, %ecx
 	xorl %eax,%eax
+	shrl $3,%ecx
 	rep stosq
 	RET
-SYM_FUNC_END(clear_page_rep)
-EXPORT_SYMBOL_GPL(clear_page_rep)
+SYM_FUNC_END(clear_pages_rep)
+EXPORT_SYMBOL_GPL(clear_pages_rep)
 
-SYM_FUNC_START(clear_page_orig)
+/*
+ * Original page zeroing loop.
+ * %rdi	- page
+ * %esi	- page-length
+ *
+ * Clobbers: %rax, %rcx, %rflags
+ */
+SYM_FUNC_START(clear_pages_orig)
+	movl   %esi, %ecx
 	xorl   %eax,%eax
-	movl   $4096/64,%ecx
+	shrl   $6,%ecx
 	.p2align 4
 .Lloop:
 	decl	%ecx
@@ -41,16 +55,23 @@ SYM_FUNC_START(clear_page_orig)
 	jnz	.Lloop
 	nop
 	RET
-SYM_FUNC_END(clear_page_orig)
-EXPORT_SYMBOL_GPL(clear_page_orig)
+SYM_FUNC_END(clear_pages_orig)
+EXPORT_SYMBOL_GPL(clear_pages_orig)
 
-SYM_FUNC_START(clear_page_erms)
-	movl $4096,%ecx
+/*
+ * Zero a page.
+ * %rdi	- page
+ * %esi	- page-length
+ *
+ * Clobbers: %rax, %rcx
+ */
+SYM_FUNC_START(clear_pages_erms)
+	movl %esi, %ecx
 	xorl %eax,%eax
 	rep stosb
 	RET
-SYM_FUNC_END(clear_page_erms)
-EXPORT_SYMBOL_GPL(clear_page_erms)
+SYM_FUNC_END(clear_pages_erms)
+EXPORT_SYMBOL_GPL(clear_pages_erms)
 
 /*
  * Default clear user-space.
-- 
2.31.1