On 22/08/2019 11:39, Jonathan Cameron wrote:

On Wed, 21 Aug 2019 16:36:51 +0100
Steven Price [off-list ref] wrote:

quoted

Implement the service call for configuring a shared structure between a
VCPU and the hypervisor in which the hypervisor can write the time
stolen from the VCPU's execution time by other tasks on the host.

The hypervisor allocates memory which is placed at an IPA chosen by user
space. The hypervisor then updates the shared structure using
kvm_put_guest() to ensure single copy atomicity of the 64-bit value
reporting the stolen time in nanoseconds.

Whenever stolen time is enabled by the guest, the stolen time counter is
reset.

The stolen time itself is retrieved from the sched_info structure
maintained by the Linux scheduler code. We enable SCHEDSTATS when
selecting KVM Kconfig to ensure this value is meaningful.

Signed-off-by: Steven Price <steven.price@arm.com>

One totally trivial comment inline... Feel free to ignore :)

[...]

quoted

+int kvm_hypercall_stolen_time(struct kvm_vcpu *vcpu)
+{
+	u64 ret;
+	int err;
+
+	/*
+	 * Start counting stolen time from the time the guest requests
+	 * the feature enabled.
+	 */
+	vcpu->arch.steal.steal = 0;
+	vcpu->arch.steal.last_steal = current->sched_info.run_delay;
+
+	err = kvm_update_stolen_time(vcpu, true);
+
+	if (err)
+		ret = SMCCC_RET_NOT_SUPPORTED;

Trivial by why not
		return SMCCC_RET_NOT_SUPPORTED;

	return vcpu->kvm->arch.pvtime.st_base +
...
Drops the indentation a bit and puts the error handling out of
line which is slightly nicer to read (to my eyes).

Yes that's a nice change - drops the extra "ret" variable too.

Thanks,

Steve

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