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SubjectRe: [PATCH 4/5] x86/mm/kaiser: Remove superfluous SWITCH_TO_KERNEL
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On 11/27/2017 02:31 PM, Peter Zijlstra wrote:
> We never use this code-path with KAISER enabled.
...
> @@ -201,14 +201,6 @@ ENTRY(entry_SYSCALL_64)
>
> swapgs
> movq %rsp, PER_CPU_VAR(rsp_scratch)
> -
> - /*
> - * The kernel CR3 is needed to map the process stack, but we
> - * need a scratch register to be able to load CR3. %rsp is
> - * clobberable right now, so use it as a scratch register.
> - * %rsp will look crazy here for a couple instructions.
> - */
> - SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
> movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp

What's the mechanism that we use to switch between the two versions of
the SYSCALL entry? It wasn't obvious from some grepping.

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