Re: [PATCH 06/24] x86,kvm: Fix indirect calls in emulator

[Peter Zijlstra]

On Tue, Jan 23, 2018 at 08:48:13PM +0000, David Woodhouse wrote:
> On Tue, 2018-01-23 at 21:28 +0100, Borislav Petkov wrote:
> > 
> > >       flags = (flags & EFLAGS_MASK) | X86_EFLAGS_IF;
> > > -     asm("push %[flags]; popf; call *%[fastop]"
> > > -         : "=a"(rc) : [fastop]"r"(fop), [flags]"r"(flags));
> > > +     asm("push %[flags]; popf; " CALL_NOSPEC
> > > +         : "=a"(rc) : [thunk_target]"r"(fop), [flags]"r"(flags));
> > 
> > Oh, "thunk_target" is magical.
> 
> You can use THUNK_TARGET(fop), which will be "rm" on 32-bit and avoids
> register starvation in some cases (I don't think the hyperv calls
> worked until I did that).

The reason I didn't use THUNK_TARGET() was exactly because it used "rm"
and the current code did "r" only. I'm happy to change if people can
agree on something ;-)