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SubjectRe: [PATCH v3 3/5] KVM: LAPIC: Expose per-vCPU timer_advance_ns to userspace
On Thu, May 16, 2019 at 11:06:18AM +0800, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> Expose per-vCPU timer_advance_ns to userspace, so it is able to
> query the auto-adjusted value.
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Sean Christopherson <sean.j.christopherson@intel.com>
> Cc: Liran Alon <liran.alon@oracle.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> arch/x86/kvm/debugfs.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/arch/x86/kvm/debugfs.c b/arch/x86/kvm/debugfs.c
> index c19c7ed..a6f1f93 100644
> --- a/arch/x86/kvm/debugfs.c
> +++ b/arch/x86/kvm/debugfs.c
> @@ -9,12 +9,22 @@
> */
> #include <linux/kvm_host.h>
> #include <linux/debugfs.h>
> +#include "lapic.h"
>
> bool kvm_arch_has_vcpu_debugfs(void)
> {
> return true;
> }
>
> +static int vcpu_get_timer_advance_ns(void *data, u64 *val)
> +{
> + struct kvm_vcpu *vcpu = (struct kvm_vcpu *) data;
> + *val = vcpu->arch.apic->lapic_timer.timer_advance_ns;

This needs to ensure to check lapic_in_kernel() to ensure apic isn't NULL.
Actually, I think we can skip creation of the parameter entirely if
lapic_in_kernel() is false. VMX and SVM both instantiate the lapic
during kvm_arch_vcpu_create(), which is (obviously) called before
kvm_arch_create_vcpu_debugfs().

> + return 0;
> +}
> +
> +DEFINE_SIMPLE_ATTRIBUTE(vcpu_timer_advance_ns_fops, vcpu_get_timer_advance_ns, NULL, "%llu\n");
> +
> static int vcpu_get_tsc_offset(void *data, u64 *val)
> {
> struct kvm_vcpu *vcpu = (struct kvm_vcpu *) data;
> @@ -51,6 +61,12 @@ int kvm_arch_create_vcpu_debugfs(struct kvm_vcpu *vcpu)
> if (!ret)
> return -ENOMEM;
>
> + ret = debugfs_create_file("lapic_timer_advance_ns", 0444,
> + vcpu->debugfs_dentry,
> + vcpu, &vcpu_timer_advance_ns_fops);
> + if (!ret)
> + return -ENOMEM;
> +
> if (kvm_has_tsc_control) {
> ret = debugfs_create_file("tsc-scaling-ratio", 0444,
> vcpu->debugfs_dentry,
> --
> 2.7.4
>

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