Re: [PATCH 02/24] x86/mm/kaiser: Prepare the x86/entry assembly code for entry/exit CR3 switching

Thomas Gleixner
2017-11-27T17:33:44Z

On Mon, 27 Nov 2017, Peter Zijlstra wrote:
> On Mon, Nov 27, 2017 at 11:49:01AM +0100, Ingo Molnar wrote:
> > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> > index caf74a1bb3de..df0152bee8a8 100644
>
> > @@ -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
> >
> > /* Construct struct pt_regs on stack */
>
> I think we can do away with this one, on account of never getting here
> because of entry_SYSCALL_64_trampoline.

It's on my list already. About 5 people noticed :)

Still trying to decode that paravirt fail.....

Thanks,

tglx