Re: [PATCH v2 18/58] i386/tdx: Validate TD attributes

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Aug 22, 2023 at 10:30:47PM +0800, Xiaoyao Li wrote:
> On 8/21/2023 5:16 PM, Daniel P. Berrangé wrote:
> > On Fri, Aug 18, 2023 at 05:50:01AM -0400, Xiaoyao Li wrote:
> > > Validate TD attributes with tdx_caps that fixed-0 bits must be zero and
> > > fixed-1 bits must be set.
> > > 
> > > Besides, sanity check the attribute bits that have not been supported by
> > > QEMU yet. e.g., debug bit, it will be allowed in the future when debug
> > > TD support lands in QEMU.
> > > 
> > > Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> > > Acked-by: Gerd Hoffmann <kraxel@redhat.com>
> > > ---
> > >   target/i386/kvm/tdx.c | 27 +++++++++++++++++++++++++--
> > >   1 file changed, 25 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
> > > index 629abd267da8..73da15377ec3 100644
> > > --- a/target/i386/kvm/tdx.c
> > > +++ b/target/i386/kvm/tdx.c
> > > @@ -32,6 +32,7 @@
> > >                                        (1U << KVM_FEATURE_PV_SCHED_YIELD) | \
> > >                                        (1U << KVM_FEATURE_MSI_EXT_DEST_ID))
> > > +#define TDX_TD_ATTRIBUTES_DEBUG             BIT_ULL(0)
> > >   #define TDX_TD_ATTRIBUTES_SEPT_VE_DISABLE   BIT_ULL(28)
> > >   #define TDX_TD_ATTRIBUTES_PKS               BIT_ULL(30)
> > >   #define TDX_TD_ATTRIBUTES_PERFMON           BIT_ULL(63)
> > > @@ -462,13 +463,32 @@ int tdx_kvm_init(MachineState *ms, Error **errp)
> > >       return 0;
> > >   }
> > > -static void setup_td_guest_attributes(X86CPU *x86cpu)
> > > +static int tdx_validate_attributes(TdxGuest *tdx)
> > > +{
> > > +    if (((tdx->attributes & tdx_caps->attrs_fixed0) | tdx_caps->attrs_fixed1) !=
> > > +        tdx->attributes) {
> > > +            error_report("Invalid attributes 0x%lx for TDX VM (fixed0 0x%llx, fixed1 0x%llx)",
> > > +                          tdx->attributes, tdx_caps->attrs_fixed0, tdx_caps->attrs_fixed1);
> > > +            return -EINVAL;
> > > +    }
> > > +
> > > +    if (tdx->attributes & TDX_TD_ATTRIBUTES_DEBUG) {
> > > +        error_report("Current QEMU doesn't support attributes.debug[bit 0] for TDX VM");
> > > +        return -EINVAL;
> > > +    }
> > 
> > Use error_setg() in both cases, passing in a 'Error **errp' object,
> > and 'return -1' instead of returning an errno value.
> > 
> 
> why return -1 instead of -EINVAL?

Returning errno values is useful if the method isn't providing an
"Error **errp" parameter, because it lets the caller report a
more detailed error message via strerror(). Once you add a Error **
parameter though, there is almost never any reason for the caller
to care about the original errno value, and so we use 0 / -1 as
success/fail indicators.

With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|