On Wed, Jan 09, 2019 at 04:01:56PM +0000, Marc Zyngier wrote:
> On 09/01/2019 14:51, Julien Thierry wrote:
> >
> >
> > On 09/01/2019 14:45, Marc Zyngier wrote:
> >> Hi Andrew,
> >>
> >> On 09/01/2019 14:24, Andrew Murray wrote:
> >>> On Wed, Jan 09, 2019 at 01:54:34PM +0000, Marc Zyngier wrote:
> >>>> When running VHE, there is no need to jump via some stub to perform
> >>>> a "HYP" function call, as there is a single address space.
> >>>>
> >>>> Let's thus change kvm_call_hyp() and co to perform a direct call
> >>>> in this case. Although this results in a bit of code expansion,
> >>>> it allows the compiler to check for type compatibility, something
> >>>> that we are missing so far.
> >>>>
> >>>> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> >>>> ---
> >>>> arch/arm64/include/asm/kvm_host.h | 32 +++++++++++++++++++++++++++++--
> >>>> 1 file changed, 30 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> >>>> index e54cb7c88a4e..df32edbadd69 100644
> >>>> --- a/arch/arm64/include/asm/kvm_host.h
> >>>> +++ b/arch/arm64/include/asm/kvm_host.h
> >>>> @@ -370,8 +370,36 @@ void kvm_arm_halt_guest(struct kvm *kvm);
> >>>> void kvm_arm_resume_guest(struct kvm *kvm);
> >>>>
> >>>> u64 __kvm_call_hyp(void *hypfn, ...);
> >>>> -#define kvm_call_hyp(f, ...) __kvm_call_hyp(kvm_ksym_ref(f), ##__VA_ARGS__)
> >>>> -#define kvm_call_hyp_ret(f, ...) kvm_call_hyp(f, ##__VA_ARGS__)
> >>>> +
> >>>> +/*
> >>>> + * The couple of isb() below are there to guarantee the same behaviour
> >>>> + * on VHE as on !VHE, where the eret to EL1 acts as a context
> >>>> + * synchronization event.
> >>>> + */
> >>>> +#define kvm_call_hyp(f, ...) \
> >>>> + do { \
> >>>> + if (cpus_have_const_cap(ARM64_HAS_VIRT_HOST_EXTN)) { \
> >>>> + f(__VA_ARGS__); \
> >>>> + isb(); \
> >>>> + } else { \
> >>>> + __kvm_call_hyp(kvm_ksym_ref(f), ##__VA_ARGS__); \
> >>>> + } \
> >>>> + } while(0)
> >>>> +
> >>>> +#define kvm_call_hyp_ret(f, ...) \
> >>>> + ({ \
> >>>> + u64 ret; \
> >>>> + \
> >>>> + if (cpus_have_const_cap(ARM64_HAS_VIRT_HOST_EXTN)) { \
> >>>> + ret = f(__VA_ARGS__); \
> >>>
> >>> __kvm_get_mdcr_el2 and __kvm_vcpu_run_nvhe don't return u64 type, they
> >>> return a smaller type. I guess any issues would be picked up when compiling,
> >>> but should the name of the macro be clearer as to the assumptions it makes?
> >>> Or perhaps take an argument which is the type of ret?
> >>
> >> kvm_call_hyp has always returned a u64, so no semantic has changed here.
Ah I missed that!
> >>
> >> Otherwise, your suggestion of specifying a return type is interesting,
> >> but it also gives the programmer another chance to shoot itself in the
> >> foot by not providing the return type corresponding to the function that
> >> is called.
> >>
> >> Unless we can extract the return type by pure magic, I'm not sure we
> >> gain much.
> >>
> >
> > Would the following work?
> >
> > typeof(f(__VA_ARGS__)) ret;
> >
> > If typeof works anything like sizeof, I'd expect it would evaluate stuff
> > passed as argument and we'd have the return type of the function.
> And it actually works! Thanks for the awful tip! ;-)
Awesome.
Thanks,
Andrew Murray
>
> M.
> --
> Jazz is not dead. It just smells funny...
