[PATCH 4/9] x86/clear_page: parameterize clear_page*() to specify length

Ankur Arora
2023-04-03T05:23:50Z

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

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.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