KVM: VMX: Open code writing vCPU's PAT in VMX's MSR handler

Open code setting "vcpu->arch.pat" in vmx_set_msr() instead of bouncing
through kvm_set_msr_common() to get to the same code in kvm_mtrr_set_msr().
This aligns VMX with SVM, avoids hiding a very simple operation behind a
relatively complicated function call (finding the PAT MSR case in
kvm_set_msr_common() is non-trivial), and most importantly, makes it clear
that not unwinding the VMCS updates if kvm_set_msr_common() isn't a bug
(because kvm_set_msr_common() can never fail for PAT).

Opportunistically set vcpu->arch.pat before updating the VMCS info so that
a future patch can move the common bits (back) into kvm_set_msr_common()
without a functional change.

Note, MSR_IA32_CR_PAT is 0x277, and is very subtly handled by

	case 0x200 ... MSR_IA32_MC0_CTL2 - 1:

in kvm_set_msr_common().

Cc: Kai Huang <kai.huang@intel.com>
Signed-off-by: Wenyao Hai <haiwenyao@uniontech.com>
[sean: massage changelog, hoist setting vcpu->arch.pat up]
Reviewed-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20230511233351.635053-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 44fb619..33b8625 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2290,16 +2290,14 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                if (!kvm_pat_valid(data))
                        return 1;
 
+               vcpu->arch.pat = data;
+
                if (is_guest_mode(vcpu) &&
                    get_vmcs12(vcpu)->vm_exit_controls & VM_EXIT_SAVE_IA32_PAT)
                        get_vmcs12(vcpu)->guest_ia32_pat = data;
 
-               if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT) {
+               if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT)
                        vmcs_write64(GUEST_IA32_PAT, data);
-                       vcpu->arch.pat = data;
-                       break;
-               }
-               ret = kvm_set_msr_common(vcpu, msr_info);
                break;
        case MSR_IA32_MCG_EXT_CTL:
                if ((!msr_info->host_initiated &&