From d3a6b6cfb82a9158ee624bf3d43e6ebd8fe05fc8 Mon Sep 17 00:00:00 2001 From: Chao Gao Date: Wed, 29 Jan 2025 11:58:57 +0200 Subject: [PATCH] KVM: x86: Allow to update cached values in kvm_user_return_msrs w/o wrmsr Several MSRs are constant and only used in userspace(ring 3). But VMs may have different values. KVM uses kvm_set_user_return_msr() to switch to guest's values and leverages user return notifier to restore them when the kernel is to return to userspace. To eliminate unnecessary wrmsr, KVM also caches the value it wrote to an MSR last time. TDX module unconditionally resets some of these MSRs to architectural INIT state on TD exit. It makes the cached values in kvm_user_return_msrs are inconsistent with values in hardware. This inconsistency needs to be fixed. Otherwise, it may mislead kvm_on_user_return() to skip restoring some MSRs to the host's values. kvm_set_user_return_msr() can help correct this case, but it is not optimal as it always does a wrmsr. So, introduce a variation of kvm_set_user_return_msr() to update cached values and skip that wrmsr. Signed-off-by: Chao Gao Signed-off-by: Isaku Yamahata Signed-off-by: Adrian Hunter Reviewed-by: Paolo Bonzini Message-ID: <20250129095902.16391-9-adrian.hunter@intel.com> Reviewed-by: Xiayao Li Signed-off-by: Paolo Bonzini --- arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/x86.c | 24 +++++++++++++++++++----- 2 files changed, 20 insertions(+), 5 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index ddb08581c64d..0c8453fa9f9e 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -2328,6 +2328,7 @@ 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); 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 8f3292ccdca4..1133bec79a82 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -636,6 +636,15 @@ static void kvm_user_return_msr_cpu_online(void) } } +static void kvm_user_return_register_notifier(struct kvm_user_return_msrs *msrs) +{ + if (!msrs->registered) { + msrs->urn.on_user_return = kvm_on_user_return; + user_return_notifier_register(&msrs->urn); + msrs->registered = true; + } +} + int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask) { struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs); @@ -649,15 +658,20 @@ int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask) return 1; msrs->values[slot].curr = value; - if (!msrs->registered) { - msrs->urn.on_user_return = kvm_on_user_return; - user_return_notifier_register(&msrs->urn); - msrs->registered = true; - } + kvm_user_return_register_notifier(msrs); 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); -- 2.50.1