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

[Janosch Frank <frankja@linux.ibm.com>]

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?

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.

> ---
>   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)