Change clear_page*() to take a length parameter.
Rename to clear_pages_*().
Signed-off-by: Ankur Arora <[email protected]>
---
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
On Sun, Apr 02, 2023 at 10:22:28PM -0700, Ankur Arora wrote:
> Change clear_page*() to take a length parameter.
> Rename to clear_pages_*().
>
> Signed-off-by: Ankur Arora <[email protected]>
> 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)
So it seems to me that clear_user_*() and clear_page_*() are now very
similar; is there really no way to de-duplicate all that?
Peter Zijlstra <[email protected]> writes:
> On Sun, Apr 02, 2023 at 10:22:28PM -0700, Ankur Arora wrote:
>> Change clear_page*() to take a length parameter.
>> Rename to clear_pages_*().
>>
>> Signed-off-by: Ankur Arora <[email protected]>
>
>> 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
> So it seems to me that clear_user_*() and clear_page_*() are now very
> similar; is there really no way to de-duplicate all that?
I'm not sure I see a good way to do that. The clear_page_*() variants
are way simpler because they don't do alignment or uacess exception
handling.
The innermost loop in them could be unified -- but both clear_pages_rep()
and clear_pages_erms() are pretty trivial.
One place where it might be worth doing is clear_user_original() and
clear_pages_orig(). These two have also diverged some (clear_pages_orig
unrolls its loop and uses a register mov):
inner loop in clear_pages_orig:
.Lloop:
decl %ecx
#define PUT(x) movq %rax,x*8(%rdi)
movq %rax,(%rdi)
PUT(1)
PUT(2)
PUT(3)
PUT(4)
PUT(5)
PUT(6)
PUT(7)
leaq 64(%rdi),%rdi
jnz .Lloop
nop
inner loop in clear_user_original:
.Lqwords:
movq $0,(%rdi)
lea 8(%rdi),%rdi
dec %rcx
jnz .Lqwords
Maybe something like this?
---
arch/x86/lib/clear_page_64.S | 35 +++++------------------------------
1 file changed, 5 insertions(+), 30 deletions(-)
diff --git a/arch/x86/lib/clear_page_64.S b/arch/x86/lib/clear_page_64.S
index 6069acf6072f..795a82214d99 100644
--- a/arch/x86/lib/clear_page_64.S
+++ b/arch/x86/lib/clear_page_64.S
@@ -28,36 +28,6 @@ SYM_FUNC_START(clear_pages_rep)
SYM_FUNC_END(clear_pages_rep)
EXPORT_SYMBOL_GPL(clear_pages_rep)
-/*
- * 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
- shrl $6,%ecx
- .p2align 4
-.Lloop:
- decl %ecx
-#define PUT(x) movq %rax,x*8(%rdi)
- movq %rax,(%rdi)
- PUT(1)
- PUT(2)
- PUT(3)
- PUT(4)
- PUT(5)
- PUT(6)
- PUT(7)
- leaq 64(%rdi),%rdi
- jnz .Lloop
- nop
- RET
-SYM_FUNC_END(clear_pages_orig)
-EXPORT_SYMBOL_GPL(clear_pages_orig)
-
/*
* Zero a page.
* %rdi - page
@@ -92,6 +62,9 @@ SYM_FUNC_START(clear_user_original)
jz .Lrest_bytes
# do the qwords first
+SYM_INNER_LABEL(clear_pages_orig, SYM_L_GLOBAL)
+ movl %esi, %ecx
+ shr $3,%rcx
.p2align 4
.Lqwords:
movq $0,(%rdi)
@@ -135,6 +108,8 @@ SYM_FUNC_START(clear_user_original)
SYM_FUNC_END(clear_user_original)
EXPORT_SYMBOL(clear_user_original)
+EXPORT_SYMBOL_GPL(clear_pages_orig)
+
/*
* Alternative clear user-space when CPU feature X86_FEATURE_REP_GOOD is
* present.