Re: [PATCH v4 3/8] KVM Guest: Add VCPU running/pre-empted state for guest

Marcelo Tosatti
2012-08-23T12:03:04Z

On Tue, Aug 21, 2012 at 04:56:35PM +0530, Nikunj A. Dadhania wrote:
> From: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>
>
> The patch adds guest code for msr between guest and hypervisor. The
> msr will export the vcpu running/pre-empted information to the guest
> from host. This will enable guest to intelligently send ipi to running
> vcpus and set flag for pre-empted vcpus. This will prevent waiting for
> vcpus that are not running.
>
> Suggested-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Signed-off-by: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>
> ---
> arch/x86/include/asm/kvm_para.h | 13 +++++++++++++
> arch/x86/kernel/kvm.c | 36 ++++++++++++++++++++++++++++++++++++
> 2 files changed, 49 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> index 2f7712e..5dfb975 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -23,6 +23,7 @@
> #define KVM_FEATURE_ASYNC_PF 4
> #define KVM_FEATURE_STEAL_TIME 5
> #define KVM_FEATURE_PV_EOI 6
> +#define KVM_FEATURE_VCPU_STATE 7
>
> /* The last 8 bits are used to indicate how to interpret the flags field
> * in pvclock structure. If no bits are set, all flags are ignored.
> @@ -39,6 +40,7 @@
> #define MSR_KVM_ASYNC_PF_EN 0x4b564d02
> #define MSR_KVM_STEAL_TIME 0x4b564d03
> #define MSR_KVM_PV_EOI_EN 0x4b564d04
> +#define MSR_KVM_VCPU_STATE 0x4b564d05
>
> struct kvm_steal_time {
> __u64 steal;
> @@ -51,6 +53,17 @@ struct kvm_steal_time {
> #define KVM_STEAL_VALID_BITS ((-1ULL << (KVM_STEAL_ALIGNMENT_BITS + 1)))
> #define KVM_STEAL_RESERVED_MASK (((1 << KVM_STEAL_ALIGNMENT_BITS) - 1 ) << 1)
>
> +struct kvm_vcpu_state {
> + __u64 state;
> + __u32 pad[14];
> +};
> +/* bits in vcpu_state->state */
> +#define KVM_VCPU_STATE_IN_GUEST_MODE 0
> +#define KVM_VCPU_STATE_SHOULD_FLUSH 1
> +
> +#define KVM_VCPU_STATE_ALIGN_BITS 5
> +#define KVM_VCPU_STATE_VALID_BITS ((-1ULL << (KVM_VCPU_STATE_ALIGN_BITS + 1)))
> +
> #define KVM_MAX_MMU_OP_BATCH 32
>
> #define KVM_ASYNC_PF_ENABLED (1 << 0)
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index c1d61ee..37e6599 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -66,6 +66,9 @@ static DEFINE_PER_CPU(struct kvm_vcpu_pv_apf_data, apf_reason) __aligned(64);
> static DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
> static int has_steal_clock = 0;
>
> +DEFINE_PER_CPU(struct kvm_vcpu_state, vcpu_state) __aligned(64);
> +static int has_vcpu_state;
> +
> /*
> * No need for any "IO delay" on KVM
> */
> @@ -302,6 +305,22 @@ static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
> apic_write(APIC_EOI, APIC_EOI_ACK);
> }
>
> +static void kvm_register_vcpu_state(void)
> +{
> + int cpu = smp_processor_id();
> + struct kvm_vcpu_state *v_state;
> +
> + if (!has_vcpu_state)
> + return;
> +
> + v_state = &per_cpu(vcpu_state, cpu);
> + memset(v_state, 0, sizeof(*v_state));
> +
> + wrmsrl(MSR_KVM_VCPU_STATE, (__pa(v_state) | KVM_MSR_ENABLED));
> + printk(KERN_INFO "kvm-vcpustate: cpu %d, msr %lx\n",
> + cpu, __pa(v_state));
> +}
> +
> void __cpuinit kvm_guest_cpu_init(void)
> {
> if (!kvm_para_available())
> @@ -330,6 +349,9 @@ void __cpuinit kvm_guest_cpu_init(void)
>
> if (has_steal_clock)
> kvm_register_steal_time();
> +
> + if (has_vcpu_state)
> + kvm_register_vcpu_state();
> }
>
> static void kvm_pv_disable_apf(void)
> @@ -393,6 +415,14 @@ void kvm_disable_steal_time(void)
> wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
> }
>
> +void kvm_disable_vcpu_state(void)
> +{
> + if (!has_vcpu_state)
> + return;
> +
> + wrmsr(MSR_KVM_VCPU_STATE, 0, 0);

wrmsrl (to be consistent).

> +}
> +
> #ifdef CONFIG_SMP
> static void __init kvm_smp_prepare_boot_cpu(void)
> {
> @@ -410,6 +440,7 @@ static void __cpuinit kvm_guest_cpu_online(void *dummy)
>
> static void kvm_guest_cpu_offline(void *dummy)
> {
> + kvm_disable_vcpu_state();

Should disable MSR at kvm_pv_guest_cpu_reboot.

> kvm_disable_steal_time();
> if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
> wrmsrl(MSR_KVM_PV_EOI_EN, 0);
> @@ -469,6 +500,11 @@ void __init kvm_guest_init(void)
> if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
> apic_set_eoi_write(kvm_guest_apic_eoi_write);
>
> +#ifdef CONFIG_PARAVIRT_TLB_FLUSH
> + if (kvm_para_has_feature(KVM_FEATURE_VCPU_STATE))
> + has_vcpu_state = 1;
> +#endif

Why only this hunk guarded by CONFIG_PARAVIRT_TLB_FLUSH and not
the rest of the code?

Is there a switch to enable/disable this feature on the kernel
command line? Grep for early_param in kvm.c.