feat(cpu): detect hypervisor on x86_64 and arm64 via CPUID #2388

whatever125 · 2025-12-07T22:44:09Z

Added detection of the virtualization platform on x86/arm64 archs using klauspost/cpuid lib.

Preserved existing s390x implementation using /proc/sysinfo.
On x86 and arm64 cpu.model.hypervisor now reports hypervisor type, or none for bare-metal, and raw CPUID string for unknown hypervisors.

Resolves #2267

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linux-foundation-easycla · 2025-12-07T22:44:15Z

The committers listed above are authorized under a signed CLA.

✅ login: whatever125 / name: Dmitry Kolmakov (6a0f931, 6a45311, 897fbc7, e448551)

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marquiz

Thanks @whatever125. A few comments below

marquiz · 2025-12-09T09:45:26Z

source/cpu/cpu.go

+		hv := strings.ToLower(cpuid.CPU.HypervisorVendorID.String())
+
+		switch hv {


Suggested change

hv := strings.ToLower(cpuid.CPU.HypervisorVendorID.String())

switch hv {

switch hv := strings.ToLower(cpuid.CPU.HypervisorVendorID.String()); hv {

marquiz · 2025-12-09T09:46:44Z

source/cpu/cpu.go

+		case "qemu":
+			return "qemu", nil
+		case "apple":
+			return "apple", nil
+		case "qnx":
+			return "qnx", nil
+		case "acrn":
+			return "acrn", nil
+		case "sre":
+			return "sre", nil


Couldn't we put all these cases where we don't mangle the value under the default case?

Suggested change

case "qemu":

return "qemu", nil

case "apple":

return "apple", nil

case "qnx":

return "qnx", nil

case "acrn":

return "acrn", nil

case "sre":

return "sre", nil

default:

return hv, nil

marquiz · 2025-12-09T09:57:49Z

source/cpu/cpu.go

+	if _, err := os.Stat("/proc/sysinfo"); err == nil {
+		data, err := os.ReadFile("/proc/sysinfo")


I wonder if it would make the code more maintainable and readable to split it into multiple functions, something like:

Suggested change

if _, err := os.Stat("/proc/sysinfo"); err == nil {

data, err := os.ReadFile("/proc/sysinfo")

if _, err := os.Stat("/proc/sysinfo"); err == nil {

return getHypervisorFromProcSysinfo

} else {

klog.Error(err, "failed to stat /proc/sysinfo")

}

if cpuid.CPU.VM() {

return getHyperVisorFromCPUID(), nil

}

return "none", nil

Also, if the stat fails, we might still want to fall back to the cpuid method (like above). Thoughts?

marquiz · 2025-12-09T09:58:54Z

/ok-to-test

whatever125 · 2025-12-09T17:40:48Z

Thank you for the feedback @marquiz. I've updated the code as you suggested:

Split into helper functions, updated fallback logic
Used default in switch case. Now only cpuid.VendorUnknown is treated separately to get vendor from cpuid.CPU.HypervisorVendorString. Otherwise, the default cpuid.CPU.HypervisorVendorID.String() is used
Got rid of string handling for simplicity and maintainability

marquiz · 2025-12-09T18:04:14Z

source/cpu/cpu.go

+		hv, discovered := getHypervisorFromProcSysinfo()
+		if discovered {
+			return hv, nil
+		}


If this does not find anything (discovered == false), do we want to fall back to getHypervisorFromCPUID()? Probably not, or WDYT?

after digging deeper, i've reconsidered the logic:

PR/SM virtualization is always present on s390x, so it should be the default fallback value (consistent with the original code)

/proc/sysinfo exists only on s390x. its absence means another arch -> go to cpuid

not being able to read it -> just log and return the error

cpuid doesn't support s390x, so we shouldn't fall back to it in any case

parsing /proc/sysinfo and not finding "Control Program:" means PR/SM virtualization by default -> return "PR/SM", not a blank string

so this is what i propose:

func getHypervisor() (string, error) { // use /proc/sysinfo for s390x if _, err := os.Stat("/proc/sysinfo"); err == nil { return getHypervisorFromProcSysinfo() } // use cpuid lib for x86/arm if cpuid.CPU.VM() { return getHypervisorFromCPUID() } // no hv discovered return "none", nil }

and then the getHypervisorFromProcSysinfo() is just the old getHypervisor().

maybe we could use runtime.GOARCH == "s390x" for a cleaner arch detection instead of doing stat on /proc/sysinfo. what do you think?

maybe we could use runtime.GOARCH == "s390x" for a cleaner arch detection instead of doing stat on /proc/sysinfo. what do you think?

That works 👍 Would make sense with the fact that /proc/sysinfo only exists on s390x

whatever125 · 2025-12-13T17:09:44Z

@marquiz thanks! i've updated the code to use runtime.GOARCH and implemented the logic we've discussed

marquiz

Nice @whatever125. This became really clean and simple.

/assign @ArangoGutierrez @fmuyassarov

k8s-ci-robot · 2025-12-15T13:21:56Z

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: marquiz, whatever125

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k8s-ci-robot requested review from adrianchiris and jjacobelli December 7, 2025 22:44

k8s-ci-robot added cncf-cla: no Indicates the PR's author has not signed the CNCF CLA. needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. labels Dec 7, 2025

k8s-ci-robot added size/M Denotes a PR that changes 30-99 lines, ignoring generated files. cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. and removed cncf-cla: no Indicates the PR's author has not signed the CNCF CLA. labels Dec 7, 2025

marquiz reviewed Dec 9, 2025

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k8s-ci-robot added ok-to-test Indicates a non-member PR verified by an org member that is safe to test. and removed needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. labels Dec 9, 2025

marquiz reviewed Dec 9, 2025

View reviewed changes

whatever125 added 4 commits December 13, 2025 20:36

feat(cpu): detect hypervisor on x86_64 and arm64 via CPUID

e448551

fix(cpu): improve hypervisor detection logic

6a45311

fix(cpu): replace klog.Error with klog.ErrorS

897fbc7

fix(cpu): use runtime.GOARCH for s390x hypervisor detection logic

6a0f931

whatever125 force-pushed the feat/cpu-detect-hypervisor-via-cpuid branch from 52a922f to 6a0f931 Compare December 13, 2025 17:36

marquiz approved these changes Dec 15, 2025

View reviewed changes

k8s-ci-robot assigned ArangoGutierrez and fmuyassarov Dec 15, 2025

k8s-ci-robot added the approved Indicates a PR has been approved by an approver from all required OWNERS files. label Dec 15, 2025

		hv := strings.ToLower(cpuid.CPU.HypervisorVendorID.String())

		switch hv {

		if _, err := os.Stat("/proc/sysinfo"); err == nil {
		data, err := os.ReadFile("/proc/sysinfo")

-	if _, err := os.Stat("/proc/sysinfo"); err == nil {
-		data, err := os.ReadFile("/proc/sysinfo")
+	if _, err := os.Stat("/proc/sysinfo"); err == nil {
+		return getHypervisorFromProcSysinfo
+	} else {
+		klog.Error(err, "failed to stat /proc/sysinfo")
+	}
+	if cpuid.CPU.VM() {
+		return getHyperVisorFromCPUID(), nil
+	}
+	return "none", nil

feat(cpu): detect hypervisor on x86_64 and arm64 via CPUID #2388

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feat(cpu): detect hypervisor on x86_64 and arm64 via CPUID #2388

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