[RFC 25/26] KVM: x86: Expose HRESET feature's CPUID to Guest

[Zhao Liu <zhao1.liu@linux.intel.com>]

From: Zhuocheng Ding <zhuocheng.ding@intel.com>

The HRESET feature needs to have not only the feature bit of 0x07.0x01.
eax[bit 22] in the CPUID, but also the associated 0x20 leaf, so, pass-
through the Host's 0x20 leaf to Guest.

Since currently, HRESET is only used to clear ITD's classification
history, only expose HRESET related CPUID when Guest has the ITD
capability.

Tested-by: Yanting Jiang <yanting.jiang@intel.com>
Signed-off-by: Zhuocheng Ding <zhuocheng.ding@intel.com>
Co-developed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
 arch/x86/kvm/cpuid.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 9e78398f29dc..726b723ee34b 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -197,6 +197,16 @@ static int kvm_check_hfi_cpuid(struct kvm_vcpu *vcpu,
 	if (data_size > hfi_features.nr_table_pages << PAGE_SHIFT)
 		return -EINVAL;
 
+	/*
+	 * Check HRESET leaf since Guest's control of MSR_IA32_HW_HRESET_ENABLE
+	 * needs to take effect on hardware.
+	 */
+	best = cpuid_entry2_find(entries, nent, 0x20, 0);
+
+	/* Cannot set the Guest bit that is unsopported by Host. */
+	if (best && best->ebx & ~cpuid_ebx(0x20))
+		return -EINVAL;
+
 	return 0;
 }
 
@@ -784,6 +794,10 @@ void kvm_set_cpu_caps(void)
 		F(AMX_FP16) | F(AVX_IFMA) | F(LAM)
 	);
 
+	/* Currently HRESET is used to reset the ITD related history. */
+	if (kvm_cpu_cap_has(X86_FEATURE_ITD))
+		kvm_cpu_cap_set(X86_FEATURE_HRESET);
+
 	kvm_cpu_cap_init_kvm_defined(CPUID_7_1_EDX,
 		F(AVX_VNNI_INT8) | F(AVX_NE_CONVERT) | F(PREFETCHITI) |
 		F(AMX_COMPLEX)
@@ -1030,7 +1044,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 	switch (function) {
 	case 0:
 		/* Limited to the highest leaf implemented in KVM. */
-		entry->eax = min(entry->eax, 0x1fU);
+		entry->eax = min(entry->eax, 0x20U);
 		break;
 	case 1:
 		cpuid_entry_override(entry, CPUID_1_EDX);
@@ -1300,6 +1314,16 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 			break;
 		}
 		break;
+	/* Intel HRESET */
+	case 0x20:
+		if (!kvm_cpu_cap_has(X86_FEATURE_HRESET)) {
+			entry->eax = 0;
+			entry->ebx = 0;
+			entry->ecx = 0;
+			entry->edx = 0;
+			break;
+		}
+		break;
 	case KVM_CPUID_SIGNATURE: {
 		const u32 *sigptr = (const u32 *)KVM_SIGNATURE;
 		entry->eax = KVM_CPUID_FEATURES;
-- 
2.34.1