Re: [Qemu-devel] [PATCH 2/9] kvm: add kvm_enable_cap_{vm,vcpu}

[Cornelia Huck]

On Wed, 16 Apr 2014 13:38:27 +0200
Alexander Graf <address@hidden> wrote:

> 
> On 16.04.2014, at 13:22, Alexander Graf <address@hidden> wrote:
> 
> > 
> > On 14.04.14 18:48, Cornelia Huck wrote:
> >> Provide helper functions for enabling capabilities (on a vcpu and on a vm).
> >> 
> >> Reviewed-by: Thomas Huth <address@hidden>
> >> Signed-off-by: Cornelia Huck <address@hidden>
> >> ---
> >>  include/sysemu/kvm.h |    4 ++++
> >>  kvm-all.c            |   33 ++++++++++++++++++++++++++++++++-
> >>  2 files changed, 36 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> >> index 0bee1e8..2ff5ad3 100644
> >> --- a/include/sysemu/kvm.h
> >> +++ b/include/sysemu/kvm.h
> >> @@ -294,6 +294,10 @@ bool kvm_arch_stop_on_emulation_error(CPUState *cpu);
> >>    int kvm_check_extension(KVMState *s, unsigned int extension);
> >>  +int kvm_enable_cap_vm(KVMState *s, unsigned int capability, ...);
> >> +
> >> +int kvm_enable_cap_vcpu(CPUState *cpu, unsigned int capability, ...);
> >> +
> >>  uint32_t kvm_arch_get_supported_cpuid(KVMState *env, uint32_t function,
> >>                                        uint32_t index, int reg);
> >>  diff --git a/kvm-all.c b/kvm-all.c
> >> index cd4111d..658e50c 100644
> >> --- a/kvm-all.c
> >> +++ b/kvm-all.c
> >> @@ -501,7 +501,38 @@ int kvm_check_extension(KVMState *s, unsigned int 
> >> extension)
> >>      return ret;
> >>  }
> >>  -static int kvm_set_ioeventfd_mmio(int fd, hwaddr addr, uint32_t val,
> >> +int kvm_enable_cap_vm(KVMState *s, unsigned int capability, ...)
> >> +{
> >> +    struct kvm_enable_cap cap = {};
> >> +    va_list ap;
> >> +    int i;
> >> +
> >> +    cap.cap = capability;
> >> +    va_start(ap, capability);
> >> +    for (i = 0; i < 4; i++) {
> >> +        cap.args[i] = va_arg(ap, uint64_t);
> > 
> > Is this legit? Can we just pull items off the stack without running beyond?
> 
> For inspiration on how to know the number of arguments that got passed in, 
> check out
> 
>   http://git.qemu.org/?p=qemu.git;a=blob;f=include/sysemu/device_tree.h#l40

Ah, that is probably better than splattering args with random stuff.
Will try.