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 <[email protected]>
>>> ---
>>> 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.
>
> 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.
Cheers,
--
Julien Thierry
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