From: Sean Christopherson <seanjc@xxxxxxxxxx> Load the guest's FPU state if userspace is accessing MSRs whose values are managed by XSAVES. Introduce two helpers, kvm_{get,set}_xstate_msr(), to facilitate access to such kind of MSRs. If MSRs supported in kvm_caps.supported_xss are passed through to guest, the guest MSRs are swapped with host's before vCPU exits to userspace and after it re-enters kernel before next VM-entry. Because the modified code is also used for the KVM_GET_MSRS device ioctl(), explicitly check @vcpu is non-null before attempting to load guest state. The XSS supporting MSRs cannot be retrieved via the device ioctl() without loading guest FPU state (which doesn't exist). Note that guest_cpuid_has() is not queried as host userspace is allowed to access MSRs that have not been exposed to the guest, e.g. it might do KVM_SET_MSRS prior to KVM_SET_CPUID2. Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> Co-developed-by: Yang Weijiang <weijiang.yang@xxxxxxxxx> Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx> --- arch/x86/kvm/x86.c | 30 +++++++++++++++++++++++++++++- arch/x86/kvm/x86.h | 24 ++++++++++++++++++++++++ 2 files changed, 53 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 66edbed25db8..a091764bf1d2 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -133,6 +133,9 @@ static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2); static void __get_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2); static DEFINE_MUTEX(vendor_module_lock); +static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu); +static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu); + struct kvm_x86_ops kvm_x86_ops __read_mostly; #define KVM_X86_OP(func) \ @@ -4372,6 +4375,22 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) } EXPORT_SYMBOL_GPL(kvm_get_msr_common); +static const u32 xstate_msrs[] = { + MSR_IA32_U_CET, MSR_IA32_PL0_SSP, MSR_IA32_PL1_SSP, + MSR_IA32_PL2_SSP, MSR_IA32_PL3_SSP, +}; + +static bool is_xstate_msr(u32 index) +{ + int i; + + for (i = 0; i < ARRAY_SIZE(xstate_msrs); i++) { + if (index == xstate_msrs[i]) + return true; + } + return false; +} + /* * Read or write a bunch of msrs. All parameters are kernel addresses. * @@ -4382,11 +4401,20 @@ static int __msr_io(struct kvm_vcpu *vcpu, struct kvm_msrs *msrs, int (*do_msr)(struct kvm_vcpu *vcpu, unsigned index, u64 *data)) { + bool fpu_loaded = false; int i; - for (i = 0; i < msrs->nmsrs; ++i) + for (i = 0; i < msrs->nmsrs; ++i) { + if (vcpu && !fpu_loaded && kvm_caps.supported_xss && + is_xstate_msr(entries[i].index)) { + kvm_load_guest_fpu(vcpu); + fpu_loaded = true; + } if (do_msr(vcpu, entries[i].index, &entries[i].data)) break; + } + if (fpu_loaded) + kvm_put_guest_fpu(vcpu); return i; } diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index 1e7be1f6ab29..9a8e3a84eaf4 100644 --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -540,4 +540,28 @@ int kvm_sev_es_string_io(struct kvm_vcpu *vcpu, unsigned int size, unsigned int port, void *data, unsigned int count, int in); +/* + * Lock and/or reload guest FPU and access xstate MSRs. For accesses initiated + * by host, guest FPU is loaded in __msr_io(). For accesses initiated by guest, + * guest FPU should have been loaded already. + */ + +static inline void kvm_get_xstate_msr(struct kvm_vcpu *vcpu, + struct msr_data *msr_info) +{ + KVM_BUG_ON(!vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm); + kvm_fpu_get(); + rdmsrl(msr_info->index, msr_info->data); + kvm_fpu_put(); +} + +static inline void kvm_set_xstate_msr(struct kvm_vcpu *vcpu, + struct msr_data *msr_info) +{ + KVM_BUG_ON(!vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm); + kvm_fpu_get(); + wrmsrl(msr_info->index, msr_info->data); + kvm_fpu_put(); +} + #endif -- 2.27.0