Re: [PATCH] KVM: x86: Only print persistent reasons for kvm disabled once

Vitaly Kuznetsov
2019-08-27T06:28:06Z

Tony Luck <tony.luck@intel.com> writes:

> When I boot my server I'm treated to a console log with:
>
> [ 40.520510] kvm: disabled by bios
> [ 40.551234] kvm: disabled by bios
> [ 40.607987] kvm: disabled by bios
> [ 40.659701] kvm: disabled by bios
> [ 40.691224] kvm: disabled by bios
> [ 40.718786] kvm: disabled by bios
> [ 40.750122] kvm: disabled by bios
> [ 40.797170] kvm: disabled by bios
> [ 40.828408] kvm: disabled by bios
>
> ... many, many more lines, one for every logical CPU

(If I didn't miss anything) we have the following code:

__init vmx_init()
kvm_init();
kvm_arch_init()

and we bail on first error so there should be only 1 message per module
load attempt. The question I have is who (and why) is trying to load
kvm-intel (or kvm-amd which is not any different) for each CPU? Is it
udev? Can this be changed?

In particular, I'm worried about eVMCS enablement in vmx_init(), we will
also get a bunch of "KVM: vmx: using Hyper-V Enlightened VMCS" messages
if the consequent kvm_arch_init() fails.

>
> Since it isn't likely that BIOS is going to suddenly enable
> KVM between bringing up one CPU and the next, we might as
> well just print this once.
>
> Same for a few other unchanging reasons that might keep
> kvm from being initialized.
>
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> ---
> arch/x86/kvm/x86.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 93b0bd45ac73..56d4a43dd2db 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7007,18 +7007,18 @@ int kvm_arch_init(void *opaque)
> struct kvm_x86_ops *ops = opaque;
>
> if (kvm_x86_ops) {
> - printk(KERN_ERR "kvm: already loaded the other module\n");
> + pr_err_once("kvm: already loaded the other module\n");
> r = -EEXIST;
> goto out;
> }
>
> if (!ops->cpu_has_kvm_support()) {
> - printk(KERN_ERR "kvm: no hardware support\n");
> + pr_err_once("kvm: no hardware support\n");
> r = -EOPNOTSUPP;
> goto out;
> }
> if (ops->disabled_by_bios()) {
> - printk(KERN_ERR "kvm: disabled by bios\n");
> + pr_err_once("kvm: disabled by bios\n");
> r = -EOPNOTSUPP;
> goto out;
> }
> @@ -7029,7 +7029,7 @@ int kvm_arch_init(void *opaque)
> * vCPU's FPU state as a fxregs_state struct.
> */
> if (!boot_cpu_has(X86_FEATURE_FPU) || !boot_cpu_has(X86_FEATURE_FXSR)) {
> - printk(KERN_ERR "kvm: inadequate fpu\n");
> + pr_err_once("kvm: inadequate fpu\n");
> r = -EOPNOTSUPP;
> goto out;
> }

The messages themselves may need some love but this is irrelevant to the
patch, so

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

--
Vitaly