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[PATCH] x86_64: Clean up copy_*_user
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- Remove optimization for old B stepping Opteron
- Make the fast path for copies with a multiple of eight length faster.
- Minor instruction rearrangement to hopefully avoid a pipeline
stall or two.
- Add comment about errata to consider.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Andi Kleen authored and Linus Torvalds committed Jan 12, 2006
1 parent 17a941d commit 2cbc9ee
Showing 1 changed file with 23 additions and 221 deletions.
244 changes: 23 additions & 221 deletions arch/x86_64/lib/copy_user.S
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Original file line number Diff line number Diff line change
Expand Up @@ -4,12 +4,9 @@
* Functions to copy from and to user space.
*/

#define FIX_ALIGNMENT 1

#include <asm/current.h>
#include <asm/asm-offsets.h>
#include <asm/thread_info.h>
#include <asm/cpufeature.h>

/* Standard copy_to_user with segment limit checking */
.globl copy_to_user
Expand All @@ -21,23 +18,7 @@ copy_to_user:
jc bad_to_user
cmpq threadinfo_addr_limit(%rax),%rcx
jae bad_to_user
2:
.byte 0xe9 /* 32bit jump */
.long .Lcug-1f
1:

.section .altinstr_replacement,"ax"
3: .byte 0xe9 /* replacement jmp with 8 bit immediate */
.long copy_user_generic_c-1b /* offset */
.previous
.section .altinstructions,"a"
.align 8
.quad 2b
.quad 3b
.byte X86_FEATURE_K8_C
.byte 5
.byte 5
.previous
jmp copy_user_generic

/* Standard copy_from_user with segment limit checking */
.globl copy_from_user
Expand Down Expand Up @@ -72,223 +53,44 @@ bad_to_user:
* rsi source
* rdx count
*
* Only 4GB of copy is supported. This shouldn't be a problem
* because the kernel normally only writes from/to page sized chunks
* even if user space passed a longer buffer.
* And more would be dangerous because both Intel and AMD have
* errata with rep movsq > 4GB. If someone feels the need to fix
* this please consider this.
*
* Output:
* eax uncopied bytes or 0 if successful.
*/
.globl copy_user_generic
.p2align 4
copy_user_generic:
.byte 0x66,0x66,0x90 /* 5 byte nop for replacement jump */
.byte 0x66,0x90
1:
.section .altinstr_replacement,"ax"
2: .byte 0xe9 /* near jump with 32bit immediate */
.long copy_user_generic_c-1b /* offset */
.previous
.section .altinstructions,"a"
.align 8
.quad copy_user_generic
.quad 2b
.byte X86_FEATURE_K8_C
.byte 5
.byte 5
.previous
.Lcug:
pushq %rbx
xorl %eax,%eax /*zero for the exception handler */

#ifdef FIX_ALIGNMENT
/* check for bad alignment of destination */
movl %edi,%ecx
andl $7,%ecx
jnz .Lbad_alignment
.Lafter_bad_alignment:
#endif

movq %rdx,%rcx

movl $64,%ebx
shrq $6,%rdx
decq %rdx
js .Lhandle_tail

.p2align 4
.Lloop:
.Ls1: movq (%rsi),%r11
.Ls2: movq 1*8(%rsi),%r8
.Ls3: movq 2*8(%rsi),%r9
.Ls4: movq 3*8(%rsi),%r10
.Ld1: movq %r11,(%rdi)
.Ld2: movq %r8,1*8(%rdi)
.Ld3: movq %r9,2*8(%rdi)
.Ld4: movq %r10,3*8(%rdi)

.Ls5: movq 4*8(%rsi),%r11
.Ls6: movq 5*8(%rsi),%r8
.Ls7: movq 6*8(%rsi),%r9
.Ls8: movq 7*8(%rsi),%r10
.Ld5: movq %r11,4*8(%rdi)
.Ld6: movq %r8,5*8(%rdi)
.Ld7: movq %r9,6*8(%rdi)
.Ld8: movq %r10,7*8(%rdi)

decq %rdx

leaq 64(%rsi),%rsi
leaq 64(%rdi),%rdi

jns .Lloop

.p2align 4
.Lhandle_tail:
movl %ecx,%edx
andl $63,%ecx
shrl $3,%ecx
jz .Lhandle_7
movl $8,%ebx
.p2align 4
.Lloop_8:
.Ls9: movq (%rsi),%r8
.Ld9: movq %r8,(%rdi)
decl %ecx
leaq 8(%rdi),%rdi
leaq 8(%rsi),%rsi
jnz .Lloop_8

.Lhandle_7:
movl %edx,%ecx
andl $7,%ecx
jz .Lende
.p2align 4
.Lloop_1:
.Ls10: movb (%rsi),%bl
.Ld10: movb %bl,(%rdi)
incq %rdi
incq %rsi
decl %ecx
jnz .Lloop_1

.Lende:
popq %rbx
ret

#ifdef FIX_ALIGNMENT
/* align destination */
.p2align 4
.Lbad_alignment:
movl $8,%r9d
subl %ecx,%r9d
movl %r9d,%ecx
cmpq %r9,%rdx
jz .Lhandle_7
js .Lhandle_7
.Lalign_1:
.Ls11: movb (%rsi),%bl
.Ld11: movb %bl,(%rdi)
incq %rsi
incq %rdi
decl %ecx
jnz .Lalign_1
subq %r9,%rdx
jmp .Lafter_bad_alignment
#endif

/* table sorted by exception address */
.section __ex_table,"a"
.align 8
.quad .Ls1,.Ls1e
.quad .Ls2,.Ls2e
.quad .Ls3,.Ls3e
.quad .Ls4,.Ls4e
.quad .Ld1,.Ls1e
.quad .Ld2,.Ls2e
.quad .Ld3,.Ls3e
.quad .Ld4,.Ls4e
.quad .Ls5,.Ls5e
.quad .Ls6,.Ls6e
.quad .Ls7,.Ls7e
.quad .Ls8,.Ls8e
.quad .Ld5,.Ls5e
.quad .Ld6,.Ls6e
.quad .Ld7,.Ls7e
.quad .Ld8,.Ls8e
.quad .Ls9,.Le_quad
.quad .Ld9,.Le_quad
.quad .Ls10,.Le_byte
.quad .Ld10,.Le_byte
#ifdef FIX_ALIGNMENT
.quad .Ls11,.Lzero_rest
.quad .Ld11,.Lzero_rest
#endif
.quad .Le5,.Le_zero
.previous

/* compute 64-offset for main loop. 8 bytes accuracy with error on the
pessimistic side. this is gross. it would be better to fix the
interface. */
/* eax: zero, ebx: 64 */
.Ls1e: addl $8,%eax
.Ls2e: addl $8,%eax
.Ls3e: addl $8,%eax
.Ls4e: addl $8,%eax
.Ls5e: addl $8,%eax
.Ls6e: addl $8,%eax
.Ls7e: addl $8,%eax
.Ls8e: addl $8,%eax
addq %rbx,%rdi /* +64 */
subq %rax,%rdi /* correct destination with computed offset */

shlq $6,%rdx /* loop counter * 64 (stride length) */
addq %rax,%rdx /* add offset to loopcnt */
andl $63,%ecx /* remaining bytes */
addq %rcx,%rdx /* add them */
jmp .Lzero_rest

/* exception on quad word loop in tail handling */
/* ecx: loopcnt/8, %edx: length, rdi: correct */
.Le_quad:
shll $3,%ecx
andl $7,%edx
addl %ecx,%edx
/* edx: bytes to zero, rdi: dest, eax:zero */
.Lzero_rest:
movq %rdx,%rcx
.Le_byte:
xorl %eax,%eax
.Le5: rep
stosb
/* when there is another exception while zeroing the rest just return */
.Le_zero:
movq %rdx,%rax
jmp .Lende

/* C stepping K8 run faster using the string copy instructions.
This is also a lot simpler. Use them when possible.
Patch in jmps to this code instead of copying it fully
to avoid unwanted aliasing in the exception tables. */

/* rdi destination
* rsi source
* rdx count
*
* Output:
* eax uncopied bytes or 0 if successfull.
*/
copy_user_generic_c:
.globl copy_user_generic
copy_user_generic:
movl %edx,%ecx
shrl $3,%ecx
andl $7,%edx
jz 5f
1: rep
movsq
movl %edx,%ecx
xor %eax,%eax
2: rep
movsb
4: movl %ecx,%eax
ret
/* align here? */
5: xorl %eax,%eax
6: rep movsq
ret

.section .fixup,"ax"
3: lea (%rdx,%rcx,8),%rax
ret

4: movl %ecx,%eax
ret
.previous

.section __ex_table,"a"
.quad 1b,3b
.quad 2b,4b
.quad 6b,4b
.previous

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