* Tony Luck <tony.l...@intel.com> wrote:
> Make use of the EXTABLE_FAULT exception table entries. This routine
> returns a structure to indicate the result of the copy:
So the series looks good to me, but I have some (mostly readability) comments
that
went beyond what I usually fix up manually:
> struct mcsafe_ret {
> u64 trapnr;
> u64 remain;
> };
> +struct mcsafe_ret {
> + u64 trapnr;
> + u64 remain;
> +};
Yeah, so please change this to something like:
struct mcsafe_ret {
u64 trap_nr;
u64 bytes_left;
};
this makes it crystal clear what the fields are about and what their unit is.
Readability is king and modern consoles are wide enough, no need to abbreviate
excessively.
> +struct mcsafe_ret __mcsafe_copy(void *dst, const void __user *src, size_t
> cnt);
> +extern void __mcsafe_copy_end(void);
So this is a bad name I think. What kind of 'copy' is this? It's defined in
asm/string_64.h - so people might thing it's a string copy. If it's a memcpy
variant then name it so.
Also, I'd suggest we postfix the new mcsafe functions with '_mcsafe', not
prefix
them. Special properties of memcpy routines are usually postfixes - such as
_nocache(), _toio(), etc.
> --- a/arch/x86/kernel/x8664_ksyms_64.c
> +++ b/arch/x86/kernel/x8664_ksyms_64.c
> @@ -37,6 +37,8 @@ EXPORT_SYMBOL(__copy_user_nocache);
> EXPORT_SYMBOL(_copy_from_user);
> EXPORT_SYMBOL(_copy_to_user);
>
> +EXPORT_SYMBOL_GPL(__mcsafe_copy);
> +
> EXPORT_SYMBOL(copy_page);
> EXPORT_SYMBOL(clear_page);
>
> diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S
> index 16698bba87de..7f967a9ed0e4 100644
> --- a/arch/x86/lib/memcpy_64.S
> +++ b/arch/x86/lib/memcpy_64.S
> @@ -177,3 +177,154 @@ ENTRY(memcpy_orig)
> .Lend:
> retq
> ENDPROC(memcpy_orig)
> +
> +#ifndef CONFIG_UML
Why is this UML quirk needed? No other memcpy functions have it. Theoretically
UML
could introduce the notion of #MC interruption.
> +/*
> + * __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 */
> + testl $7,%esi
> + /* already aligned */
> + jz 102f
> +
> + /* copy one byte at a time until source is 8-byte aligned */
> + movl %esi,%ecx
> + andl $7,%ecx
> + subl $8,%ecx
> + negl %ecx
> + subl %ecx,%edx
> +0: movb (%rsi),%al
> + movb %al,(%rdi)
> + incq %rsi
> + incq %rdi
> + decl %ecx
> + jnz 0b
> +
> +102:
> + /* Figure out how many whole cache lines (64-bytes) to copy */
> + movl %edx,%ecx
> + andl $63,%edx
> + shrl $6,%ecx
> + jz 17f
Please don't use numeric labels in new assembly code, use descriptively named
local labels:
.L_do_stuff:
numeric labels are generally unfriendly against future changes. They are the
GOTO
numeric labels of BASIC.
> +
> + /* Loop copying whole cache lines */
> +1: movq (%rsi),%r8
> +2: movq 1*8(%rsi),%r9
> +3: movq 2*8(%rsi),%r10
> +4: movq 3*8(%rsi),%r11
> + movq %r8,(%rdi)
> + movq %r9,1*8(%rdi)
> + movq %r10,2*8(%rdi)
> + movq %r11,3*8(%rdi)
> +9: movq 4*8(%rsi),%r8
> +10: movq 5*8(%rsi),%r9
> +11: movq 6*8(%rsi),%r10
> +12: movq 7*8(%rsi),%r11
> + movq %r8,4*8(%rdi)
> + movq %r9,5*8(%rdi)
> + movq %r10,6*8(%rdi)
> + movq %r11,7*8(%rdi)
> + leaq 64(%rsi),%rsi
> + leaq 64(%rdi),%rdi
> + decl %ecx
> + jnz 1b
> +
> + /* Are there any trailing 8-byte words? */
> +17: movl %edx,%ecx
> + andl $7,%edx
> + shrl $3,%ecx
> + jz 20f
> +
> + /* Copy trailing words */
> +18: movq (%rsi),%r8
> + mov %r8,(%rdi)
> + leaq 8(%rsi),%rsi
> + leaq 8(%rdi),%rdi
> + decl %ecx
> + jnz 18b
> +
> + /* Any trailing bytes? */
> +20: andl %edx,%edx
> + jz 23f
> +
> + /* copy trailing bytes */
> + movl %edx,%ecx
> +21: movb (%rsi),%al
> + movb %al,(%rdi)
> + incq %rsi
> + incq %rdi
> + decl %ecx
> + jnz 21b
> +
> + /* Copy successful. Return .remain = 0, .trapnr = 0 */
> +23: xorq %rax, %rax
> + xorq %rdx, %rdx
> + ret
> +
> + .section .fixup,"ax"
> + /*
> + * machine check handler loaded %rax with trap number
> + * We just need to make sure %edx has the number of
> + * bytes remaining
> + */
Please use consistent capitalization in comments and punctuate sentences where
there's more than one of them.
Thanks,
Ingo
