Re: [Xen-devel] [PATCH v3 1/5] x86/boot: Only jump into low trampoline code for real-mode boot

[David Woodhouse <dwmw2@xxxxxxxxxxxxx>]

On Fri, 2019-08-30 at 16:25 +0200, Jan Beulich wrote:
> On 21.08.2019 18:35, David Woodhouse wrote:
> > --- a/xen/arch/x86/boot/head.S
> > +++ b/xen/arch/x86/boot/head.S
> > @@ -727,7 +727,17 @@ trampoline_setup:
> >          /* Switch to low-memory stack which lives at the end of
> > trampoline region. */
> >          mov     sym_fs(trampoline_phys),%edi
> >          lea     TRAMPOLINE_SPACE+TRAMPOLINE_STACK_SPACE(%edi),%esp
> > +        cmpb    $0, sym_fs(skip_realmode)
> > +        jz      1f
> > +        /* If no-real-mode, jump straight to
> > trampoline_protmode_entry */
> > +        lea     trampoline_protmode_entry-
> > trampoline_start(%edi),%eax
> > +        /* EBX == 0 indicates we are the BP (Boot Processor). */
> > +        xor     %ebx,%ebx
> > +        jmp     2f
> > +1:
> > +        /* Go via 16-bit code in trampoline_boot_cpu_entry */
> >          lea     trampoline_boot_cpu_entry-
> > trampoline_start(%edi),%eax
> > +2:
> >          pushl   $BOOT_CS32
> >          push    %eax
> 
> Provided it goes in together with the subsequent change removing this
> double jump again
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Thanks.

> Of course it would have been nice if within you addition you'd been
> consistent with adding (or not) blanks after commas separating insn
> operands.

Yeah, I can see how that would be useful. I'll do it as I rebase on top
of the current staging branch and redo the conflict resolution with
Andy's changes.

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