From 9bc366350734246301b090802fc71f9924daad39 Mon Sep 17 00:00:00 2001 From: Hou Wenlong Date: Tue, 23 Sep 2025 08:37:37 -0700 Subject: [PATCH] KVM: x86: Add helper to retrieve current value of user return MSR In the user return MSR support, the cached value is always the hardware value of the specific MSR. Therefore, add a helper to retrieve the cached value, which can replace the need for RDMSR, for example, to allow SEV-ES guests to restore the correct host hardware value without using RDMSR. Cc: stable@vger.kernel.org Signed-off-by: Hou Wenlong [sean: drop "cache" from the name, make it a one-liner, tag for stable] Reviewed-by: Xiaoyao Li Link: https://lore.kernel.org/r/20250923153738.1875174-2-seanjc@google.com Signed-off-by: Sean Christopherson --- arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/x86.c | 6 ++++++ 2 files changed, 7 insertions(+) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 822a5596a4a0..0d6a4af79b78 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -2357,6 +2357,7 @@ 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); +u64 kvm_get_user_return_msr(unsigned int slot); static inline bool kvm_is_supported_user_return_msr(u32 msr) { diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 1d7faf8bc785..5ac2183b9993 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -677,6 +677,12 @@ void kvm_user_return_msr_update_cache(unsigned int slot, u64 value) } EXPORT_SYMBOL_GPL(kvm_user_return_msr_update_cache); +u64 kvm_get_user_return_msr(unsigned int slot) +{ + return this_cpu_ptr(user_return_msrs)->values[slot].curr; +} +EXPORT_SYMBOL_GPL(kvm_get_user_return_msr); + static void drop_user_return_notifiers(void) { struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs); -- 2.47.3