Re: [PATCH 3/6] qemu: check if AMD secure guest support is enabled

On 5/13/20 1:21 AM, Erik Skultety wrote: >>>>> 2) check if /dev/sev device exist (aka firmware is detected) >>>> This seems reasonable. Shouldn't it have been documented in >>>> docs/kbase/launch_security_sev.rst? >>> Sure, we can add a mention about this. Although, doesn't 1 imply 2? IOW can >>> you have the kernel module parameter set to 1 and yet kernel doesn't expose the >>> /dev/sev node? >> >> Currently, 1 does not imply 2, KVM driver does not initialize the >> firmware during the feature probe (i.e does not access the /dev/sev). >> The firmware initialization is delayed until the first guest launch. So >> only sane way to know whether firmware is been detected is check the >> existence of the /dev/sev or issue a query-sev command . The query-sev >> command will send the platform_status request to the firmware, if the >> firmware is not ready then this command will fail. > I see. Can query-sev fail or return that it's disabled, aka {"enabled": > false,...} in the SevInfo QMP response, but at the same time succeed in > returning the platform capabilities via query-sev-capabilities? I'm asking, > because libvirt only issues the latter to fill in the QEMU capabilities > structure. Just looked at qemu code, If /dev/sev does not exist then query-sev-capabilities should fail, and if SEV is not enabled in the guest then query-sev should returns false. So, basically what libvirt is doing correct, it should be using query-sev-capabilities to populate QEMU capabilities. It was my bad, I should have mentioned the query-sev-capabilities and not the query-sev check.