Re: [PATCH v2 2/6] KVM-HV: KVM Steal time implementation

From: Avi Kivity
Date: Sun Jan 30 2011 - 08:13:45 EST

On 01/28/2011 09:52 PM, Glauber Costa wrote:
To implement steal time, we need the hypervisor to pass the guest information
about how much time was spent running other processes outside the VM.
This is per-vcpu, and using the kvmclock structure for that is an abuse
we decided not to make.

In this patchset, I am introducing a new msr, KVM_MSR_STEAL_TIME, that
holds the memory area address containing information about steal time

This patch contains the hypervisor part for it. I am keeping it separate from
the headers to facilitate backports to people who wants to backport the kernel
part but not the hypervisor, or the other way around.

@@ -1528,16 +1528,23 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
vcpu->arch.time_page =
gfn_to_page(vcpu->kvm, data>> PAGE_SHIFT);

- if (is_error_page(vcpu->arch.time_page)) {
- kvm_release_page_clean(vcpu->arch.time_page);
- vcpu->arch.time_page = NULL;
- }


@@ -2106,6 +2120,25 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
vcpu->cpu = cpu;
+ if (vcpu->arch.this_time_out) {
+ u64 to = (get_kernel_ns() - vcpu->arch.this_time_out);
+ /*
+ * using nanoseconds introduces noise, which accumulates easily
+ * leading to big steal time values. We want, however, to keep the
+ * interface nanosecond-based for future-proofness.
+ */
+ to /= NSEC_PER_USEC;
+ to *= NSEC_PER_USEC;

Seems there is a real problem and that this is just papering it over. I'd like to understand the root cause.

+ vcpu->arch.time_out += to;
+ kvm_write_guest(vcpu->kvm, (gpa_t)&st->steal,
+ &vcpu->arch.time_out, sizeof(st->steal));

Error check.

+ vcpu->arch.sversion += 2;

Doesn't survive live migration. You need to use the version from the guest area.

+ kvm_write_guest(vcpu->kvm, (gpa_t)&st->version,
+ &vcpu->arch.sversion, sizeof(st->version));
+ /* is it possible to have 2 loads in sequence? */
+ vcpu->arch.this_time_out = 0;
+ }

error compiling committee.c: too many arguments to function

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