Re: [PATCH v2 2/4] s390x/pv: Check for support on the host

[Cédric Le Goater]

On 1/9/23 09:45, Janosch Frank wrote:
> On 1/6/23 08:53, Cédric Le Goater wrote:
> > From: Cédric Le Goater <clg@redhat.com>
> >
> > Support for protected VMs should have been enabled on the host with
> > the kernel parameter 'prot_virt=1'. If the hardware supports the
> > feature, it is reflected under sysfs.
> >
> > Reviewed-by: Thomas Huth <thuth@redhat.com>
> > Signed-off-by: Cédric Le Goater <clg@redhat.com>
>
> Any reason why you didn't use KVM_CAP_S390_PROTECTED?

I think my setup was incorrect when I did the patch. I just verified and QEMU
indeed reports :

 qemu-system-s390x: CPU model does not support Protected Virtualization

which means S390_FEAT_UNPACK was not set.


> The sysfs interface isn't meant to be parsed by programs, it's been introduced 
> for humans. Most of the interface's data has therefore been made available via 
> the UV info API.

Well, QEMU is user space and does peek around in sysfs to collect some info.
Unneeded in that case.

Thanks,

C.



> > ---
> >   hw/s390x/pv.c | 23 ++++++++++++++++++++++-
> >   1 file changed, 22 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/s390x/pv.c b/hw/s390x/pv.c
> > index 8a1c71436b..d53ef8fd38 100644
> > --- a/hw/s390x/pv.c
> > +++ b/hw/s390x/pv.c
> > @@ -14,6 +14,7 @@
> >   #include <linux/kvm.h>
> >   #include "qapi/error.h"
> > +#include "qemu/cutils.h"
> >   #include "qemu/error-report.h"
> >   #include "sysemu/kvm.h"
> >   #include "qom/object_interfaces.h"
> > @@ -280,9 +281,29 @@ static bool s390_pv_check_cpus(Error **errp)
> >       return true;
> >   }
> > +#define S390_PV_HOST "/sys/firmware/uv/prot_virt_host"
> > +
> > +static bool s390_pv_check_host(Error **errp)
> > +{
> > +    gchar *s = NULL;
> > +    uint64_t pv_host = 0;
> > +
> > +    if (g_file_get_contents(S390_PV_HOST, &s, NULL, NULL)) {
> > +        pv_host = g_ascii_strtoull(s, NULL, 10);
> > +    }
> > +    g_free(s);
> > +
> > +    if (pv_host != 1) {
> > +        error_setg(errp, "Host does not support protected VMs");
> > +        return false;
> > +    }
> > +
> > +    return true;
> > +}
> > +
> >   static bool s390_pv_guest_check(ConfidentialGuestSupport *cgs, Error **errp)
> >   {
> > -    return s390_pv_check_cpus(errp);
> > +    return s390_pv_check_cpus(errp) && s390_pv_check_host(errp);
> >   }
> >   int s390_pv_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)