linux-kernel - [PATCH v2 1/8] KVM: VMX: Open code writing vCPU's PAT in VMX's MSR handler

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Message-ID: <20230511233351.635053-2-seanjc@google.com>
Date:   Thu, 11 May 2023 16:33:44 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kai Huang <kai.huang@...el.com>,
        Wenyao Hai <haiwenyao@...ontech.com>,
        Ke Guo <guoke@...ontech.com>
Subject: [PATCH v2 1/8] KVM: VMX: Open code writing vCPU's PAT in VMX's MSR handler

From: Wenyao Hai <haiwenyao@...ontech.com>

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@...el.com>
Signed-off-by: Wenyao Hai <haiwenyao@...ontech.com>
[sean: massage changelog, hoist setting vcpu->arch.pat up]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/vmx.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 44fb619803b8..33b8625d3541 100644
--- 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 &&
-- 
2.40.1.606.ga4b1b128d6-goog