Re: [PATCH v4 14/17] x86/asm/entry/64: Migrate error and interrupt exit work to C

Borislav Petkov
2015-07-02T12:10:03Z

On Mon, Jun 29, 2015 at 12:33:46PM -0700, Andy Lutomirski wrote:
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> arch/x86/entry/entry_64.S | 63 +++++++++++-----------------------------
> arch/x86/entry/entry_64_compat.S | 5 ++++
> 2 files changed, 22 insertions(+), 46 deletions(-)
>
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index ce2c9049abef..08a37ec049f0 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -508,7 +508,16 @@ END(irq_entries_start)
>
> testb $3, CS(%rsp)
> jz 1f
> +
> + /*
> + * IRQ from user mode. Switch to kernel gsbase and inform context
> + * tracking that we're in kernel mode.
> + */
> SWAPGS
> +#ifdef CONFIG_CONTEXT_TRACKING
> + call enter_from_user_mode
> +#endif

I think you can make this much cleaner by getting rid of the ifdeffery
and pushing it into the enter_from_user_mode() function:

__visible void enter_from_user_mode(void)
{
#ifdef CONFIG_CONTEXT_TRACKING

...

#endif
}

The disadvantage of all that cleanliness is that we get one dumb

call enter_from_user_mode

there to this abomination:

ffffffff810014f0 <enter_from_user_mode>:
ffffffff810014f0: e8 db 97 67 00 callq ffffffff8167acd0 <__fentry__>
ffffffff810014f5: 55 push %rbp
ffffffff810014f6: 48 89 e5 mov %rsp,%rbp
ffffffff810014f9: 5d pop %rbp
ffffffff810014fa: c3 retq
ffffffff810014fb: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)

which sux.

We sure could use LTO here.

--
Regards/Gruss,
Boris.

ECO tip #101: Trim your mails when you reply.
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