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

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.