KVM: x86: Remove defunct setting of XCR0 for guest during vCPU create

Drop code to initialize XCR0 during fx_init(), a.k.a. vCPU creation, as
XCR0 has been initialized during kvm_vcpu_reset() (for RESET) since
commit a554d207 ("KVM: X86: Processor States following Reset or INIT").

Back when XCR0 support was added by commit 2acf923e ("KVM: VMX:
Enable XSAVE/XRSTOR for guest"), KVM didn't differentiate between RESET
and INIT.  Ignoring the fact that calling fx_init() for INIT is obviously
wrong, e.g. FPU state after INIT is not the same as after RESET, setting
XCR0 in fx_init() was correct.

Eventually fx_init() got moved to kvm_arch_vcpu_init(), a.k.a. vCPU
creation (ignore the terrible name) by commit 0ee6a517 ("x86/fpu,
kvm: Simplify fx_init()").  Finally, commit 95a0d01e ("KVM: x86: Move
all vcpu init code into kvm_arch_vcpu_create()") killed off
kvm_arch_vcpu_init(), leaving behind the oddity of redundant setting of
guest state during vCPU creation.

No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210921000303.400537-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -973,7 +973,7 @@ static int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
 	/*
 	 * Do not allow the guest to set bits that we do not support
 	 * saving.  However, xcr0 bit 0 is always set, even if the
-	 * emulated CPU does not support XSAVE (see fx_init).
+	 * emulated CPU does not support XSAVE (see kvm_vcpu_reset()).
 	 */
 	valid_bits = vcpu->arch.guest_supported_xcr0 | XFEATURE_MASK_FP;
 	if (xcr0 & ~valid_bits)
@@ -10606,11 +10606,6 @@ static void fx_init(struct kvm_vcpu *vcpu)
 	if (boot_cpu_has(X86_FEATURE_XSAVES))
 		vcpu->arch.guest_fpu->state.xsave.header.xcomp_bv =
 			host_xcr0 | XSTATE_COMPACTION_ENABLED;
-
-	/*
-	 * Ensure guest xcr0 is valid for loading
-	 */
-	vcpu->arch.xcr0 = XFEATURE_MASK_FP;
 }
 
 void kvm_free_guest_fpu(struct kvm_vcpu *vcpu)