Re: WARNING: can't access registers at asm_common_interrupt

[Peter Zijlstra]

On Wed, Nov 18, 2020 at 07:47:36AM +0100, Jürgen Groß wrote:
> On 16.11.20 14:04, Peter Zijlstra wrote:
> > On Mon, Nov 16, 2020 at 12:56:32PM +0100, Jürgen Groß wrote:
> > > > > > > > > static inline notrace unsigned long arch_local_save_flags(void)
> > > > > > > > > {
> > > > > > > > >      PVOP_CALL_ARGS;
> > > > > > > > >      PVOP_TEST_NULL(irq.save_fl);
> > > > > > > > >      asm_inline volatile(ALTERNATIVE(paravirt_alt(PARAVIRT_CALL),
> > > > > > > > >                                      "PUSHF; POP _ASM_AX",
> > > > > > > > >                                      X86_FEATURE_NATIVE)
> > > 
> > > I am wondering whether we really want a new feature (basically "not
> > > XENPV). We could use ~X86_FEATURE_XENPV and teach apply_alternatives()
> > > to understand negated features (yes, this limits the number of features
> > > to 32767, but I don't think this is a real problem for quite some time).
> > > 
> > > Thoughts?
> > 
> > I went with the simple thing for now... If we ever want/need another
> > negative alternative I suppose we can do as you suggest...
> > 
> > I was still poking at objtool to actually dtrt though..
> 
> I'd like to include this part in my series (with a different solution
> for the restore_fl part, as suggested by Andy before).
> 
> Peter, are you fine with me taking your patch and adding your SoB?

Sure, note that I only compile tested it, as it was my test-bed for
playing with objtool (which I still haven't managed to get back to and
finish :/).

So if it actually _works_ feel free to take it, otherwise you can have
whatever bits and pieces remain after you've butchered it to do as you
want.