Re: [PATCH v2 3/3] x86/pti/64: Remove the SYSCALL64 entry trampoline

Borislav Petkov
2018-09-07T09:36:09Z

On Mon, Sep 03, 2018 at 03:59:44PM -0700, Andy Lutomirski wrote:
> The SYSCALL64 trampoline has a couple of nice properties:
>
> - The usual sequence of SWAPGS followed by two GS-relative accesses to
> set up RSP is somewhat slow because the GS-relative accesses need
> to wait for SWAPGS to finish. The trampoline approach allows
> RIP-relative accesses to set up RSP, which avoids the stall.

...

> diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
> index 31341ae7309f..7e79154846c8 100644
> --- a/arch/x86/mm/pti.c
> +++ b/arch/x86/mm/pti.c
> @@ -434,11 +434,42 @@ static void __init pti_clone_p4d(unsigned long addr)
> }
>
> /*
> - * Clone the CPU_ENTRY_AREA into the user space visible page table.
> + * Clone the CPU_ENTRY_AREA and associated data into the user space visible
> + * page table.
> */
> static void __init pti_clone_user_shared(void)
> {
> + unsigned cpu;

Make that

unsigned int cpu;

Otherwise, patches removing complex code are always good!

Reviewed-by: Borislav Petkov <bp@suse.de>

--
Regards/Gruss,
Boris.

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