KVM: x86: Replace (almost) all guest CPUID feature queries with cpu_caps

Switch all queries (except XSAVES) of guest features from guest CPUID to
guest capabilities, i.e. replace all calls to guest_cpuid_has() with calls
to guest_cpu_cap_has().

Keep guest_cpuid_has() around for XSAVES, but subsume its helper
guest_cpuid_get_register() and add a compile-time assertion to prevent
using guest_cpuid_has() for any other feature.  Add yet another comment
for XSAVE to explain why KVM is allowed to query its raw guest CPUID.

Opportunistically drop the unused guest_cpuid_clear(), as there should be
no circumstance in which KVM needs to _clear_ a guest CPUID feature now
that everything is tracked via cpu_caps.  E.g. KVM may need to _change_
a feature to emulate dynamic CPUID flags, but KVM should never need to
clear a feature in guest CPUID to prevent it from being used by the guest.

Delete the last remnants of the governed features framework, as the lone
holdout was vmx_adjust_secondary_exec_control()'s divergent behavior for
governed vs. ungoverned features.

Note, replacing guest_cpuid_has() checks with guest_cpu_cap_has() when
computing reserved CR4 bits is a nop when viewed as a whole, as KVM's
capabilities are already incorporated into the calculation, i.e. if a
feature is present in guest CPUID but unsupported by KVM, its CR4 bit
was already being marked as reserved, checking guest_cpu_cap_has() simply
double-stamps that it's a reserved bit.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20241128013424.4096668-51-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 4d5cf6c3894f..d0df4f9ad4a7 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -437,7 +437,7 @@ void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	 * and can install smaller shadow pages if the host lacks 1GiB support.
 	 */
 	allow_gbpages = tdp_enabled ? boot_cpu_has(X86_FEATURE_GBPAGES) :
-				      guest_cpuid_has(vcpu, X86_FEATURE_GBPAGES);
+				      guest_cpu_cap_has(vcpu, X86_FEATURE_GBPAGES);
 	guest_cpu_cap_change(vcpu, X86_FEATURE_GBPAGES, allow_gbpages);
 
 	best = kvm_find_cpuid_entry(vcpu, 1);
@@ -462,7 +462,7 @@ void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 
 #define __kvm_cpu_cap_has(UNUSED_, f) kvm_cpu_cap_has(f)
 	vcpu->arch.cr4_guest_rsvd_bits = __cr4_reserved_bits(__kvm_cpu_cap_has, UNUSED_) |
-					 __cr4_reserved_bits(guest_cpuid_has, vcpu);
+					 __cr4_reserved_bits(guest_cpu_cap_has, vcpu);
 #undef __kvm_cpu_cap_has
 
 	kvm_hv_set_cpuid(vcpu, kvm_cpuid_has_hyperv(vcpu));