Re: [libvirt] [PATCH v2] qemu: Add check for whether KVM nesting is enabled

On 11/28/18 5:02 AM, Daniel P. Berrangé wrote: > On Tue, Nov 27, 2018 at 02:15:39PM -0500, John Ferlan wrote: >> >> >> On 11/27/18 12:05 PM, Andrea Bolognani wrote: >>> On Mon, 2018-11-26 at 18:38 -0500, John Ferlan wrote: >>> [...] >>>> +static bool >>>> +virQEMUCapsKVMIsNested(void) >>>> +{ >>>> + VIR_AUTOFREE(char *) kConfig = NULL; >>>> + >>>> + /* Intel, AMD, and s390 related checks */ >>>> + if ((kConfig = virKModConfig()) && >>>> + (strstr(kConfig, "kvm_intel nested=1") || >>>> + strstr(kConfig, "kvm_amd nested=1") || >>>> + strstr(kConfig, "kvm nested=1"))) >>>> + return true; >>>> + return false; >>>> +} >>> >>> I might be doing it wrong, but I'm pretty sure I've enabled nested >>> virtualization properly on my laptop given that I can successfully >>> run 'modprobe kvm_intel' inside the L1 guest, and yet I get >>> >>> # modprobe -c | grep -c nested=1 >>> 0 >>> >>> both in the L0 host and the L1 guest, so this check doesn't seem >>> accurate to me. >>> >>> Oh, wait, I get it now: 'modprobe -c' doesn't dump the *current* host >>> configuration, but the *static* one! So if you enable nested KVM >>> support by doing >>> >>> # modprobe -r kvm_intel >>> # modprobe kvm_intel nested=1 >>> >>> like I did, then the check above will not report it as enabled even >>> though it is; conversely, if you drop the appropriate config snippet >>> in /etc/modprobe.d/ but don't reload the module it will report it as >>> enabled even though it's not! >> >> Ugh, sigh... Yep, I was thinking primarily the static config option >> since we had helpers to read. Of course that won't be enough. Joy, more >> code to probe... Maybe it is easier to just say - clear your >> capabilities cache if you alter that particular kernel value. > > Surely its already easier just to ask the kernel for the live status > > $ cat /sys/module/kvm_intel/parameters/nested > 1 > My commentary was more towards I was hoping to "reuse" the exising kmod helpers ;-) before I had thought about or written any code to read the live data. The other "annoying" part is that you have "1" in your output and I have "Y" or "N". So much for "consistency".