linux-kernel - [PATCH] KVM: x86: Drop "cache" from user return MSR setter that skips WRMSR

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Message-ID: <20250919214259.1584273-1-seanjc@google.com>
Date: Fri, 19 Sep 2025 14:42:59 -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, 
	Yan Zhao <yan.y.zhao@...el.com>, Xiaoyao Li <xiaoyao.li@...el.com>, 
	Rick Edgecombe <rick.p.edgecombe@...el.com>
Subject: [PATCH] KVM: x86: Drop "cache" from user return MSR setter that skips WRMSR

Rename kvm_user_return_msr_update_cache() to __kvm_set_user_return_msr()
and use the helper kvm_set_user_return_msr() to make it obvious that the
double-underscores version is doing a subset of the work of the "full"
setter.

While the function does indeed update a cache, the nomenclature becomes
slightly misleading when adding a getter[1], as the current value isn't
_just_ the cached value, it's also the value that's currently loaded in
hardware.

Opportunistically rename "index" to "slot" in the prototypes.  The user-
return APIs deliberately use "slot" to try and make it more obvious that
they take the slot within the array, not the index of the MSR.

No functional change intended.

Cc: Yan Zhao <yan.y.zhao@...el.com>
Cc: Xiaoyao Li <xiaoyao.li@...el.com>
Cc: Rick Edgecombe <rick.p.edgecombe@...el.com>
Link: https://lore.kernel.org/all/aM2EvzLLmBi5-iQ5@google.com [1]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/kvm_host.h |  4 ++--
 arch/x86/kvm/vmx/tdx.c          |  4 ++--
 arch/x86/kvm/x86.c              | 21 ++++++++++-----------
 3 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 17772513b9cc..b633d5c33f57 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2374,8 +2374,8 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
 
 int kvm_add_user_return_msr(u32 msr);
 int kvm_find_user_return_msr(u32 msr);
-int kvm_set_user_return_msr(unsigned index, u64 val, u64 mask);
-void kvm_user_return_msr_update_cache(unsigned int index, u64 val);
+int kvm_set_user_return_msr(unsigned int slot, u64 val, u64 mask);
+void __kvm_set_user_return_msr(unsigned int slot, u64 val);
 
 static inline bool kvm_is_supported_user_return_msr(u32 msr)
 {
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index ff41d3d00380..b3cb39ae937d 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -809,8 +809,8 @@ static void tdx_user_return_msr_update_cache(void)
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++)
-		kvm_user_return_msr_update_cache(tdx_uret_msrs[i].slot,
-						 tdx_uret_msrs[i].defval);
+		__kvm_set_user_return_msr(tdx_uret_msrs[i].slot,
+					  tdx_uret_msrs[i].defval);
 }
 
 static void tdx_prepare_switch_to_host(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e07936efacd4..d975d0c60107 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -648,6 +648,15 @@ static void kvm_user_return_register_notifier(struct kvm_user_return_msrs *msrs)
 	}
 }
 
+void __kvm_set_user_return_msr(unsigned int slot, u64 value)
+{
+	struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs);
+
+	msrs->values[slot].curr = value;
+	kvm_user_return_register_notifier(msrs);
+}
+EXPORT_SYMBOL_GPL(__kvm_set_user_return_msr);
+
 int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask)
 {
 	struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs);
@@ -660,21 +669,11 @@ int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask)
 	if (err)
 		return 1;
 
-	msrs->values[slot].curr = value;
-	kvm_user_return_register_notifier(msrs);
+	__kvm_set_user_return_msr(slot, value);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(kvm_set_user_return_msr);
 
-void kvm_user_return_msr_update_cache(unsigned int slot, u64 value)
-{
-	struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs);
-
-	msrs->values[slot].curr = value;
-	kvm_user_return_register_notifier(msrs);
-}
-EXPORT_SYMBOL_GPL(kvm_user_return_msr_update_cache);
-
 static void drop_user_return_notifiers(void)
 {
 	struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs);

base-commit: c8fbf7ceb2ae3f64b0c377c8c21f6df577a13eb4
-- 
2.51.0.470.ga7dc726c21-goog