Linux Adding New Interface For Reporting AMD SEV Status

A convenient addition that surprisingly hasn't been added to the Linux kernel until now is /sys/devices/system/cpu/sev/sev_status as a new sysfs interface for reporting the AMD Secure Encrypted Virtualization (SEV) status. A patch is now queued in the x86/sev Git branch of tip/tip.git for the Linux 7.4 kernel to introduce /sys/devices/system/cpu/sev/sev_status. This new sysfs file will report the status of the SEV_MSR register for guest VMs. This makes it easy for easily determining the status of SEV VM encryption without having to resort to other user-space utilities (sevctl, snpguest, etc) or the like. The SEV_STATUS model specific register can indicate not only if SEV is active but the higher bits can also indicate the active capabilities such as for SEV-ES and SEV-SNP features. This small but helpful addition introducing the sev_status sysfs can be found by this patch ahead of the Linux 7.4 kernel cycle kicking off in October.