On Fri, Jan 08, 2016 at 01:18:03PM -0800, Tony Luck wrote:
> Make use of the EXTABLE_FAULT exception table entries. This routine
> returns a structure to indicate the result of the copy:
>
> struct mcsafe_ret {
> u64 trapnr;
> u64 remain;
> };
>
> If the copy is successful, then both 'trapnr' and 'remain' are zero.
>
> If we faulted during the copy, then 'trapnr' will say which type
> of trap (X86_TRAP_PF or X86_TRAP_MC) and 'remain' says how many
> bytes were not copied.
>
> Note that this is probably the first of several copy functions.
> We can make new ones for non-temporal cache handling etc.
>
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
> arch/x86/include/asm/string_64.h | 8 +++
> arch/x86/kernel/x8664_ksyms_64.c | 2 +
> arch/x86/lib/memcpy_64.S | 134 +++++++++++++++++++++++++++++++++++++++
> 3 files changed, 144 insertions(+)
...
> diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S
> index 16698bba87de..f576acad485e 100644
> --- a/arch/x86/lib/memcpy_64.S
> +++ b/arch/x86/lib/memcpy_64.S
> @@ -177,3 +177,137 @@ ENTRY(memcpy_orig)
> .Lend:
> retq
> ENDPROC(memcpy_orig)
> +
> +#ifndef CONFIG_UML
> +/*
> + * __mcsafe_copy - memory copy with machine check exception handling
> + * Note that we only catch machine checks when reading the source addresses.
> + * Writes to target are posted and don't generate machine checks.
> + */
> +ENTRY(__mcsafe_copy)
> + cmpl $8,%edx
> + jb 20f /* less then 8 bytes, go to byte copy loop */
> +
> + /* check for bad alignment of source */
> + movl %esi,%ecx
You can save yourself this MOV here in what is, I'm assuming, the
general likely case where @src is aligned and do:
/* check for bad alignment of source */
testl $7, %esi
/* already aligned? */
jz 102f
movl %esi,%ecx
subl $8,%ecx
negl %ecx
subl %ecx,%edx
0: movb (%rsi),%al
movb %al,(%rdi)
incq %rsi
incq %rdi
decl %ecx
jnz 0b
> + andl $7,%ecx
> + jz 102f /* already aligned */
Please move side-comments over the line they're referring to.
> + subl $8,%ecx
> + negl %ecx
> + subl %ecx,%edx
> +0: movb (%rsi),%al
> + movb %al,(%rdi)
> + incq %rsi
> + incq %rdi
> + decl %ecx
> + jnz 0b
> +102:
> + movl %edx,%ecx
> + andl $63,%edx
> + shrl $6,%ecx
> + jz 17f
Please add a \n after the JMPs for better readability - those blocks are
dense as it is. They could use some comments too.
> +1: movq (%rsi),%r8
> +2: movq 1*8(%rsi),%r9
> +3: movq 2*8(%rsi),%r10
> +4: movq 3*8(%rsi),%r11
> + mov %r8,(%rdi)
> + mov %r9,1*8(%rdi)
> + mov %r10,2*8(%rdi)
> + mov %r11,3*8(%rdi)
You can say "movq" too here, for consistency.
> +9: movq 4*8(%rsi),%r8
> +10: movq 5*8(%rsi),%r9
> +11: movq 6*8(%rsi),%r10
> +12: movq 7*8(%rsi),%r11
Why aren't we pushing %r12-%r15 on the stack after the "jz 17f" above
and using them too and thus copying a whole cacheline in one go?
We would need to restore them when we're done with the cacheline-wise
shuffle, of course.
> + mov %r8,4*8(%rdi)
> + mov %r9,5*8(%rdi)
> + mov %r10,6*8(%rdi)
> + mov %r11,7*8(%rdi)
> + leaq 64(%rsi),%rsi
> + leaq 64(%rdi),%rdi
> + decl %ecx
> + jnz 1b
...
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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