Re: [RFC PATCH] x86 NMI-safe INT3 and Page Fault (v7)

[Jeremy Fitzhardinge]

Mathieu Desnoyers wrote:
> * Jeremy Fitzhardinge (jeremy@xxxxxxxx) wrote:
>   
> > Mathieu Desnoyers wrote:
> >     
> > > +/*
> > > + * Only returns from a trap or exception to a NMI context 
> > > (intra-privilege
> > > + * level near return) to the same SS and CS segments. Should be used
> > > + * upon trap or exception return when nested over a NMI context so no 
> > > iret is
> > > + * issued. It takes care of modifying the eflags, rsp and returning to 
> > > the
> > > + * previous function.
> > > + *
> > > + * The stack, at that point, looks like :
> > > + *
> > > + * 0(rsp)  RIP
> > > + * 8(rsp)  CS
> > > + * 16(rsp) EFLAGS
> > > + * 24(rsp) RSP
> > > + * 32(rsp) SS
> > > + *
> > > + * Upon execution :
> > > + * Copy EIP to the top of the return stack
> > > + * Update top of return stack address
> > > + * Pop eflags into the eflags register
> > > + * Make the return stack current
> > > + * Near return (popping the return address from the return stack)
> > > + */
> > > +#define INTERRUPT_RETURN_NMI_SAFE	pushq %rax;		\
> > > +					mov %rsp, %rax;		\
> > > +					mov 24+8(%rax), %rsp;	\
> > > +					pushq 0+8(%rax);	\
> > > +					pushq 16+8(%rax);	\
> > > +					movq (%rax), %rax;	\
> > > +					popfq;			\
> > > +					ret;
> > >   
> > >       
> > I got this right first go?  I must be getting good at this...
> >
> >     
>
> Yes, it looked good to me at least :)
>
>   
> > Anyway, trailing ';', and perhaps use a consistent form for mov (either 
> > movq or mov in all three instances).
> >
> >     
>
> Ok, fixed. Here is the update.
>
> The last issue standing would be the paravirt code. Any ideas about how
> it's best to do it ? It would be good to be able to get the nmi-safe
> version on bare metal, patched with a standard iret emulation in
> paravirt code.
>   

#ifdef CONFIG_PARAVIRT
#define NMI_RETURN   paravirt_nmi_return

/* elsewhere */
   .nmi_return = native_iret_nmi_return;
#else
#define NMI_RETURN   NMI_SAFE_NMI_RETURN
#endif

?

   J
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