linux-kernel - [PATCH v5 09/23] KVM: VMX: Add host MSR read/write helpers to streamline preemption logic

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Message-ID: <20250723175341.1284463-10-xin@zytor.com>
Date: Wed, 23 Jul 2025 10:53:27 -0700
From: "Xin Li (Intel)" <xin@...or.com>
To: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org
Cc: pbonzini@...hat.com, seanjc@...gle.com, corbet@....net, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, xin@...or.com, luto@...nel.org,
        peterz@...radead.org, andrew.cooper3@...rix.com, chao.gao@...el.com,
        hch@...radead.org
Subject: [PATCH v5 09/23] KVM: VMX: Add host MSR read/write helpers to streamline preemption logic

From: Sean Christopherson <seanjc@...gle.com>

Introduce helper functions for host MSR access to centralize and simplify
preemption handling.  This improves code readability and reduces duplication,
laying the groundwork for a cleaner implementation of FRED RSP0 access
functions in the following patch.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Xin Li (Intel) <xin@...or.com>
---
 arch/x86/kvm/vmx/vmx.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 1e58d61dc021..53dce136e24b 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1358,22 +1358,35 @@ static void vmx_prepare_switch_to_host(struct vcpu_vmx *vmx)
 }
 
 #ifdef CONFIG_X86_64
-static u64 vmx_read_guest_kernel_gs_base(struct vcpu_vmx *vmx)
+static u64 vmx_read_guest_host_msr(struct vcpu_vmx *vmx, u32 msr, u64 *cache)
 {
 	preempt_disable();
 	if (vmx->vt.guest_state_loaded)
-		rdmsrq(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base);
+		*cache = read_msr(msr);
 	preempt_enable();
-	return vmx->msr_guest_kernel_gs_base;
+	return *cache;
 }
 
-static void vmx_write_guest_kernel_gs_base(struct vcpu_vmx *vmx, u64 data)
+static void vmx_write_guest_host_msr(struct vcpu_vmx *vmx, u32 msr, u64 data,
+				     u64 *cache)
 {
 	preempt_disable();
 	if (vmx->vt.guest_state_loaded)
-		wrmsrq(MSR_KERNEL_GS_BASE, data);
+		wrmsrns(msr, data);
 	preempt_enable();
-	vmx->msr_guest_kernel_gs_base = data;
+	*cache = data;
+}
+
+static u64 vmx_read_guest_kernel_gs_base(struct vcpu_vmx *vmx)
+{
+	return vmx_read_guest_host_msr(vmx, MSR_KERNEL_GS_BASE,
+				       &vmx->msr_guest_kernel_gs_base);
+}
+
+static void vmx_write_guest_kernel_gs_base(struct vcpu_vmx *vmx, u64 data)
+{
+	vmx_write_guest_host_msr(vmx, MSR_KERNEL_GS_BASE, data,
+				 &vmx->msr_guest_kernel_gs_base);
 }
 #endif
 
-- 
2.50.1