Re: [PATCH: kvm 3/5] Fix hotadd of CPUs for KVM.

Avi Kivity
2009-09-27T08:52:27Z

On 09/25/2009 03:47 AM, Zachary Amsden wrote:
> Both VMX and SVM require per-cpu memory allocation, which is done at module
> init time, for only online cpus. When bringing a new CPU online, we must
> also allocate this structure. The method chosen to implement this is to
> make the CPU online notifier available via a call to the arch code. This
> allows memory allocation to be done smoothly, without any need to allocate
> extra structures.
>
> Note: CPU up notifiers may call KVM callback before calling cpufreq callbacks.
> This would causes the CPU frequency not to be detected (and it is not always
> clear on non-constant TSC platforms what the bringup TSC rate will be, so the
> guess of using tsc_khz could be wrong). So, we clear the rate to zero in such
> a case and add logic to query it upon entry.
>
> Signed-off-by: Zachary Amsden<zamsden@redhat.com>
> ---
> arch/x86/include/asm/kvm_host.h | 2 ++
> arch/x86/kvm/svm.c | 15 +++++++++++++--
> arch/x86/kvm/vmx.c | 17 +++++++++++++++++
> arch/x86/kvm/x86.c | 13 +++++++++----
> include/linux/kvm_host.h | 6 ++++++
> virt/kvm/kvm_main.c | 6 ++----
> 6 files changed, 49 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 299cc1b..b7dd14b 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -459,6 +459,7 @@ struct descriptor_table {
> struct kvm_x86_ops {
> int (*cpu_has_kvm_support)(void); /* __init */
> int (*disabled_by_bios)(void); /* __init */
> + int (*cpu_hotadd)(int cpu);
> int (*hardware_enable)(void *dummy);
> void (*hardware_disable)(void *dummy);
> void (*check_processor_compatibility)(void *rtn);
> @@ -791,6 +792,7 @@ asmlinkage void kvm_handle_fault_on_reboot(void);
> _ASM_PTR " 666b, 667b \n\t" \
> ".popsection"
>
> +#define KVM_ARCH_WANT_HOTPLUG_NOTIFIER
> #define KVM_ARCH_WANT_MMU_NOTIFIER
> int kvm_unmap_hva(struct kvm *kvm, unsigned long hva);
> int kvm_age_hva(struct kvm *kvm, unsigned long hva);
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 9a4daca..8f99d0c 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -330,13 +330,13 @@ static int svm_hardware_enable(void *garbage)
> return -EBUSY;
>
> if (!has_svm()) {
> - printk(KERN_ERR "svm_cpu_init: err EOPNOTSUPP on %d\n", me);
> + printk(KERN_ERR "svm_hardware_enable: err EOPNOTSUPP on %d\n", me);
> return -EINVAL;
> }
> svm_data = per_cpu(svm_data, me);
>
> if (!svm_data) {
> - printk(KERN_ERR "svm_cpu_init: svm_data is NULL on %d\n",
> + printk(KERN_ERR "svm_hardware_enable: svm_data is NULL on %d\n",
> me);
> return -EINVAL;
> }
> @@ -394,6 +394,16 @@ err_1:
>
> }
>
> +static __cpuinit int svm_cpu_hotadd(int cpu)
> +{
> + struct svm_cpu_data *svm_data = per_cpu(svm_data, cpu);
> +
> + if (svm_data)
> + return 0;
> +
> + return svm_cpu_init(cpu);
> +}
> +
> static void set_msr_interception(u32 *msrpm, unsigned msr,
> int read, int write)
> {
> @@ -2858,6 +2868,7 @@ static struct kvm_x86_ops svm_x86_ops = {
> .hardware_setup = svm_hardware_setup,
> .hardware_unsetup = svm_hardware_unsetup,
> .check_processor_compatibility = svm_check_processor_compat,
> + .cpu_hotadd = svm_cpu_hotadd,
> .hardware_enable = svm_hardware_enable,
> .hardware_disable = svm_hardware_disable,
> .cpu_has_accelerated_tpr = svm_cpu_has_accelerated_tpr,
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 3fe0d42..b8a8428 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -1408,6 +1408,22 @@ static __exit void hardware_unsetup(void)
> free_kvm_area();
> }
>
> +static __cpuinit int vmx_cpu_hotadd(int cpu)
> +{
> + struct vmcs *vmcs;
> +
> + if (per_cpu(vmxarea, cpu))
> + return 0;
> +
> + vmcs = alloc_vmcs_cpu(cpu);
> + if (!vmcs)
> + return -ENOMEM;
> +
> + per_cpu(vmxarea, cpu) = vmcs;
> +
> + return 0;
> +}
> +
> static void fix_pmode_dataseg(int seg, struct kvm_save_segment *save)
> {
> struct kvm_vmx_segment_field *sf =&kvm_vmx_segment_fields[seg];
> @@ -3925,6 +3941,7 @@ static struct kvm_x86_ops vmx_x86_ops = {
> .hardware_setup = hardware_setup,
> .hardware_unsetup = hardware_unsetup,
> .check_processor_compatibility = vmx_check_processor_compat,
> + .cpu_hotadd = vmx_cpu_hotadd,
> .hardware_enable = hardware_enable,
> .hardware_disable = hardware_disable,
> .cpu_has_accelerated_tpr = report_flexpriority,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c18e2fc..66c6bb9 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1326,6 +1326,8 @@ out:
> void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> {
> kvm_x86_ops->vcpu_load(vcpu, cpu);
> + if (unlikely(per_cpu(cpu_tsc_khz, cpu) == 0))
> + per_cpu(cpu_tsc_khz, cpu) = cpufreq_quick_get(cpu);
> kvm_request_guest_time_update(vcpu);
> }
>
> @@ -4699,12 +4701,15 @@ int kvm_arch_vcpu_reset(struct kvm_vcpu *vcpu)
> return kvm_x86_ops->vcpu_reset(vcpu);
> }
>
> +int kvm_arch_cpu_hotadd(int cpu)
> +{
> + if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
> + per_cpu(cpu_tsc_khz, cpu) = 0;
> + return kvm_x86_ops->cpu_hotadd(cpu);
> +}
> +
> int kvm_arch_hardware_enable(void *garbage)
> {
> - if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
> - int cpu = raw_smp_processor_id();
> - per_cpu(cpu_tsc_khz, cpu) = cpufreq_quick_get(cpu);
> - }
> return kvm_x86_ops->hardware_enable(garbage);
> }
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 0bf9ee9..2f075c4 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -345,6 +345,12 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id);
> int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu);
> void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu);
>
> +#ifdef KVM_ARCH_WANT_HOTPLUG_NOTIFIER
> +int kvm_arch_cpu_hotadd(int cpu);
> +#else
> +#define kvm_arch_cpu_hotadd(x) (0)
> +#endif
> +
> int kvm_arch_vcpu_reset(struct kvm_vcpu *vcpu);
> int kvm_arch_hardware_enable(void *garbage);
> void kvm_arch_hardware_disable(void *garbage);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index e27b7a9..7818b51 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1716,9 +1716,6 @@ static int kvm_cpu_hotplug(struct notifier_block *notifier, unsigned long val,
> {
> int cpu = (long)v;
>
> - if (!kvm_usage_count)
> - return NOTIFY_OK;
> -
>

Why? You'll now do hardware_enable() even if kvm is not in use.

> val&= ~CPU_TASKS_FROZEN;
> switch (val) {
> case CPU_DYING:
> @@ -1734,7 +1731,8 @@ static int kvm_cpu_hotplug(struct notifier_block *notifier, unsigned long val,
> case CPU_ONLINE:
> printk(KERN_INFO "kvm: enabling virtualization on CPU%d\n",
> cpu);
> - smp_call_function_single(cpu, hardware_enable, NULL, 1);
> + if (!kvm_arch_cpu_hotadd(cpu))
> + smp_call_function_single(cpu, hardware_enable, NULL, 1);
> break;
> }
>

if (!blah) when blah is not a boolean or a pointer is confusing.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.