Re: [PATCH] KVM-USER: Check kvm extensions at runtime

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Gregory Haskins wrote:
> Newer userspace may run on an older kernel.  Therefore we need a way to 
> check the capabilities of the kernel so that we can downgrade userspace
> dynamically if necessary
>
> Signed-off-by: Gregory Haskins <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org>
> ---
>
>  qemu/qemu-kvm.c |   19 +++++++++++++++++++
>  user/kvmctl.c   |   14 ++++++++++++++
>  user/kvmctl.h   |    5 +++++
>  3 files changed, 38 insertions(+), 0 deletions(-)
>
> diff --git a/qemu/qemu-kvm.c b/qemu/qemu-kvm.c
> index 59e79bf..6096f21 100644
> --- a/qemu/qemu-kvm.c
> +++ b/qemu/qemu-kvm.c
> @@ -697,6 +697,25 @@ int kvm_qemu_init()
>  int kvm_qemu_create_context(void)
>  {
>      int i;
> +    uint64_t ext;
> +
> +    if (kvm_check_extension(kvm_context, &ext) < 0) {
> +	kvm_qemu_destroy();
> +	return -1;
> +    }
> +
> +    if (!(ext & KVM_EXTENSION_LAPIC) && kvm_apic_level) {
> +	/*
> +	 * Opps... the kernel doesnt support apic-emulation even though
> +	 * the user wants it.  We must turn this off and warn the user
> +	 */
> +	kvm_apic_level = 0;
> +
> +	/* FIXME: We should log this officially */
> +	printf("WARNING: older kernel does not support apic " \
> +	       "emulation.  Falling back to userspace emulation.  Upgrade " \
> +	       "your kernel/modules\n");
> +    }
>   

The user may not be in a position to upgrade the kernel.  Think distro 
kernel and userspace.  A warning is a bit severe.

>  
>      if (kvm_create(kvm_context, phys_ram_size, kvm_apic_level,
>  		   (void**)&phys_ram_base) < 0) {
> diff --git a/user/kvmctl.c b/user/kvmctl.c
> index ea86426..fcabc1a 100644
> --- a/user/kvmctl.c
> +++ b/user/kvmctl.c
> @@ -889,3 +889,17 @@ int kvm_set_signal_mask(kvm_context_t kvm, int vcpu, const sigset_t *sigset)
>  	free(sigmask);
>  	return r;
>  }
> +
> +int kvm_check_extension(kvm_context_t kvm, uint64_t *ext)
> +{
> +	*ext = 0;
> +
> +	int r = ioctl(kvm->fd, KVM_CHECK_EXTENSION, KVM_APIC_MSG);
> +	if (r < 0)
> +		return r;
>   

-errno for new code, please.

> +
> +	if (r)
> +		*ext |= KVM_EXTENSION_LAPIC;
> +
> +	return 0;
> +}
>   

How about a struct with a field per extension instead of bitmasks?

-- 
error compiling committee.c: too many arguments to function


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