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

[Peter Zijlstra]

On Wed, Jan 24, 2018 at 11:43:05AM +0100, Paolo Bonzini wrote:
> On 24/01/2018 11:35, Peter Zijlstra wrote:
> > 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 ;-)
> 
> In practice, "fastop" is going to be in a register because of how it's
> computed, but "rm" is okay.

OK, so the other occurence in that file uses "+S", which is the SI
register. That cannot use THUNK_TARGET(), right?

So do you want one THUNK_TARGET and one open coded, or keep the patch as
is (both open coded) ?