[PATCH RESEND] KVM: x86/pmu: Make top-down.slots event unavailable in supported leaf

[Like Xu]

From: Like Xu <likexu@xxxxxxxxxxx>

When we choose to disable the fourth fixed counter TOPDOWN.SLOTS,
we need to also reduce the length of the 0AH.EBX bit vector, which
enumerates architecture performance monitoring events, and set
0AH.EBX.[bit 7] to 1 if the new value of EAX[31:24] is still > 7.

Fixes: 2e8cd7a3b8287 ("kvm: x86: limit the maximum number of vPMU fixed counters to 3")
Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
---
 arch/x86/kvm/cpuid.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 0b920e12bb6d..1f0131145296 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -782,6 +782,21 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		eax.split.mask_length = cap.events_mask_len;
 
 		edx.split.num_counters_fixed = min(cap.num_counters_fixed, MAX_FIXED_COUNTERS);
+
+		/*
+		 * The 8th Intel pre-defined architectural event (Topdown Slots) will be supported
+		 * if the 4th fixed counter exists && EAX[31:24] > 7 && EBX[7] = 0.
+		 *
+		 * Currently, KVM needs to set EAX[31:24] < 8 or EBX[7] == 1
+		 * to make this event unavailable in a consistent way.
+		 */
+		if (edx.split.num_counters_fixed < 4) {
+			if (eax.split.mask_length > 7)
+				eax.split.mask_length--;
+			if (eax.split.mask_length > 7)
+				cap.events_mask |= BIT_ULL(7);
+		}
+
 		edx.split.bit_width_fixed = cap.bit_width_fixed;
 		if (cap.version)
 			edx.split.anythread_deprecated = 1;
-- 
2.33.1