Re: [Qemu-devel] [PATCH for-2.9? v2] kvm: Print MSR information if KVM_{GET, SET}_MSRS failed

[Eduardo Habkost]

On Thu, Mar 09, 2017 at 08:08:00PM +0000, Dr. David Alan Gilbert wrote:
> * Eduardo Habkost (address@hidden) wrote:
> > When a KVM_{GET,SET}_MSRS ioctl() fails, it is difficult to find
> > out which MSR caused the problem. Print an error message for
> > debugging, before we trigger the (ret == cpu->kvm_msr_buf->nmsrs)
> > assert.
> > 
> > Suggested-by: Dr. David Alan Gilbert <address@hidden>
> > Signed-off-by: Eduardo Habkost <address@hidden>
> 
> Thanks!
> 
> Reviewed-by: Dr. David Alan Gilbert <address@hidden>
> 
> I'd actually suggest it for 2.9; it's only added debug output.

I think I agree. The patch is reasonably safe because we would be
already hitting the assert() if (ret < cpu->kvm_msr_buf->nmsrs)
anyway.

Paolo, do you want to queue it for 2.9?

> 
> Dave
> 
> > ---
> > Changes v1 -> v2:
> > * Print error message on KVM_GET_MSRS too
> >   * Suggested-by: Dr. David Alan Gilbert <address@hidden>
> > ---
> >  target/i386/kvm.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> > index 887a81268f..705e971a63 100644
> > --- a/target/i386/kvm.c
> > +++ b/target/i386/kvm.c
> > @@ -1807,6 +1807,12 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
> >          return ret;
> >      }
> >  
> > +    if (ret < cpu->kvm_msr_buf->nmsrs) {
> > +        struct kvm_msr_entry *e = &cpu->kvm_msr_buf->entries[ret];
> > +        error_report("error: failed to set MSR 0x%" PRIx32 " to 0x%" 
> > PRIx64,
> > +                     (uint32_t)e->index, (uint64_t)e->data);
> > +    }
> > +
> >      assert(ret == cpu->kvm_msr_buf->nmsrs);
> >      return 0;
> >  }
> > @@ -2172,6 +2178,12 @@ static int kvm_get_msrs(X86CPU *cpu)
> >          return ret;
> >      }
> >  
> > +    if (ret < cpu->kvm_msr_buf->nmsrs) {
> > +        struct kvm_msr_entry *e = &cpu->kvm_msr_buf->entries[ret];
> > +        error_report("error: failed to get MSR 0x%" PRIx32,
> > +                     (uint32_t)e->index);
> > +    }
> > +
> >      assert(ret == cpu->kvm_msr_buf->nmsrs);
> >      /*
> >       * MTRR masks: Each mask consists of 5 parts
> > -- 
> > 2.11.0.259.g40922b1
> > 
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK

-- 
Eduardo