Re: [PATCH] x86_64,xen,espfix: Initialize espfix on secondary CPUs

[Boris Ostrovsky]

On 07/15/2014 11:38 AM, Konrad Rzeszutek Wilk wrote:
> On Tue, Jul 15, 2014 at 08:26:41AM -0700, Andy Lutomirski wrote:
> > Xen doesn't call start_secondary.
> Duh!
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> > ---
> >
> > espfix still doesn't seem to work on Xen (it goes boom in some way that
> > I don't understand right now), but initializing all CPUs instead of just
> > one of them seems like a good start.
> >
> > ISTM the right fix is probably to shove the espfix logic into
> > native_iret and to tweak the paravirt logic so that native_iret always
> > gets invoked.  I suspect that Xen will need its own implementation of
> > espfix64 in the hypervisor and that, ultimately, someone may want to
> > stop initializing espfix64 at all on Xen guests.
> I think just disallowing would be preferrable.

I've been looking at sigreturn_64 and it seems to be crashing dom0 (with 
both mine and your patches). In kprobe_int3_handler().


-boris

> Thanks for posting this patch!
> >   arch/x86/xen/smp.c | 8 ++++++++
> >   1 file changed, 8 insertions(+)
> >
> > diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> > index 7005974..eea9bcc 100644
> > --- a/arch/x86/xen/smp.c
> > +++ b/arch/x86/xen/smp.c
> > @@ -23,6 +23,7 @@
> >   #include <asm/desc.h>
> >   #include <asm/pgtable.h>
> >   #include <asm/cpu.h>
> > +#include <asm/espfix.h>
> >   
> >   #include <xen/interface/xen.h>
> >   #include <xen/interface/vcpu.h>
> > @@ -85,6 +86,13 @@ static void cpu_bringup(void)
> >   
> >   	xen_setup_cpu_clockevents();
> >   
> > +	/*
> > +	 * Enable the espfix hack for this CPU
> > +	 */
> > +#ifdef CONFIG_X86_ESPFIX64
> > +	init_espfix_ap();
> > +#endif
> > +
> >   	notify_cpu_starting(cpu);
> >   
> >   	set_cpu_online(cpu, true);
> > --
> > 1.9.3

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