Linux Will Finally Indicate Via /proc/cpuinfo If AMD SVM Virtualization Is Disabled

Checking for the presence of Intel virtualization (VMX) support and it being enabled can be easily achieved by looking at the flags in /proc/cpuinfo. But to this point AMD virtualization (SVM) has always been shown to user-space via /proc/cpuinfo even when the BIOS/platform has disabled SVM functionality. Finally for Linux 6.7 this oversight is being corrected.

Beginning with the upcoming Linux 6.7 kernel cycle -- though potentially back-ported as a fix to existing kernel series -- is a patch from Red Hat to no longer advertise SVM via /proc/cpuinfo for cases where SVM is disabled in the BIOS. This matches the behavior of Intel VMX not appearing via /proc/cpuinfo either when it's been disabled by the platform/BIOS, which makes it much easier to check if virtualization is available via this convenient and widely-used interface.

This patch by Red Hat's Paolo Bonzini has been queued into TIP's x86/cpu branch ahead of the Linux 6.7 merge window coming up in about one month. For AMD (and Hygon) processors it will now read the appropriate MSR to verify whether SVM has been disabled -- and if so to clear the CPU capability so it won't show in /proc/cpuinfo. Up to now the only indication of AMD SVM being disabled by the BIOS was appearing in the kernel log -- or simply KVM virtualization failing to work. A small but useful change.