[RFC PATCH 1/3] KVM: x86: Add helpers for {set|clear} bits in supported_xss

[Yang Weijiang]

From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

KVM supported XSS feature bits are designated in supported_xss, bits
could be set/cleared dynamically, add helpers to facilitate the operation.
Also add MSR_IA32_XSS to the list of MSRs reported to userspace if
supported_xss is non-zero, i.e. KVM supports at least one XSS based
feature.

Co-developed-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
 arch/x86/kvm/x86.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 397f599b20e5..528eba526c9c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1237,6 +1237,8 @@ static const u32 msrs_to_save_all[] = {
 	MSR_ARCH_PERFMON_EVENTSEL0 + 12, MSR_ARCH_PERFMON_EVENTSEL0 + 13,
 	MSR_ARCH_PERFMON_EVENTSEL0 + 14, MSR_ARCH_PERFMON_EVENTSEL0 + 15,
 	MSR_ARCH_PERFMON_EVENTSEL0 + 16, MSR_ARCH_PERFMON_EVENTSEL0 + 17,
+
+	MSR_IA32_XSS,
 };
 
 static u32 msrs_to_save[ARRAY_SIZE(msrs_to_save_all)];
@@ -5728,6 +5730,10 @@ static void kvm_init_msr_list(void)
 			    min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp))
 				continue;
 			break;
+		case MSR_IA32_XSS:
+			if (!supported_xss)
+				continue;
+			break;
 		default:
 			break;
 		}
@@ -10137,6 +10143,18 @@ void kvm_arch_hardware_disable(void)
 	drop_user_return_notifiers();
 }
 
+static inline void __maybe_unused kvm_set_xss_bits(u32 low, u32 high)
+{
+	supported_xss |= low;
+	supported_xss |= ((u64)high) << 32;
+}
+
+static inline void __maybe_unused kvm_clear_xss_bits(u32 low, u32 high)
+{
+	supported_xss &= ~low;
+	supported_xss &= ~(((u64)high) << 32);
+}
+
 int kvm_arch_hardware_setup(void *opaque)
 {
 	struct kvm_x86_init_ops *ops = opaque;
@@ -10155,6 +10173,8 @@ int kvm_arch_hardware_setup(void *opaque)
 
 	if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
 		supported_xss = 0;
+	else
+		supported_xss &= host_xss;
 
 #define __kvm_cpu_cap_has(UNUSED_, f) kvm_cpu_cap_has(f)
 	cr4_reserved_bits = __cr4_reserved_bits(__kvm_cpu_cap_has, UNUSED_);
-- 
2.17.2