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SubjectRe: [PATCH v2 04/44] x86/asm/head: use a common function for starting CPUs
On 4 August 2016 at 17:22, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> There are two different pieces of code for starting a CPU: start_cpu0()
> and the end of secondary_startup_64(). They're identical except for the
> stack setup. Combine the common parts into a shared start_cpu()
> function.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
> arch/x86/kernel/head_64.S | 18 ++++++++----------
> 1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index aa10a53..8822c20 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -264,13 +264,15 @@ ENTRY(secondary_startup_64)
> movl $MSR_GS_BASE,%ecx
> movl initial_gs(%rip),%eax
> movl initial_gs+4(%rip),%edx
> - wrmsr
> + wrmsr
>
> /* rsi is pointer to real mode structure with interesting info.
> pass it to C */
> movq %rsi, %rdi
> -
> - /* Finally jump to run C code and to be on real kernel address
> +
> +ENTRY(start_cpu)
> + /*
> + * Jump to run C code and to be on a real kernel address.
> * Since we are running on identity-mapped space we have to jump
> * to the full 64bit address, this is only possible as indirect
> * jump. In addition we need to ensure %cs is set so we make this
> @@ -307,15 +309,11 @@ ENDPROC(secondary_startup_64)
> /*
> * Boot CPU0 entry point. It's called from play_dead(). Everything has been set
> * up already except stack. We just set up stack here. Then call
> - * start_secondary().
> + * start_secondary() via start_cpu().
> */
> ENTRY(start_cpu0)
> - movq initial_stack(%rip),%rsp
> - movq initial_code(%rip),%rax
> - pushq $0 # fake return address to stop unwinder
> - pushq $__KERNEL_CS # set correct cs
> - pushq %rax # target address in negative space
> - lretq
> + movq initial_stack(%rip), %rsp
> + jmp start_cpu
> ENDPROC(start_cpu0)
> #endif
>

I have small suggestion here. To me jumping from start_cpu0 into the
middle of secondary_startup_64 just seems strange. May be we can
define separate ENTRY and ENDPROC pair for start_cpu and jump there
from start_cpu0 and also from secondary_startup_64.

--
Nilay

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