Messages in this thread | | | Date | Mon, 27 Nov 2017 14:36:47 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH v2] x86/mm/kaiser: Prepare the x86/entry assembly code for entry/exit CR3 switching |
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On Mon, 27 Nov 2017, Josh Poimboeuf wrote: > On Sun, Nov 26, 2017 at 03:55:53PM +0100, Ingo Molnar wrote: > > @@ -198,6 +201,14 @@ 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 > > I think it doesn't make sense to have a SWITCH_TO_KERNEL_CR3 here. This > code is the (future) kaiser-disabled path, where SWITCH_TO_KERNEL_CR3 is > a no-op anyway.
Yes, Borislav noticed that as well. That's a left over from the early versions where the trampoline did not exist.
Thanks,
tglx
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