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From: Yang Weijiang <weijiang.yang@intel.com>
To: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	pbonzini@redhat.com, sean.j.christopherson@intel.com,
Cc: yu.c.zhang@linux.intel.com, Yang Weijiang <weijiang.yang@intel.com>
Subject: [PATCH v13 06/11] KVM: x86: Load guest fpu state when access MSRs managed by XSAVES
Date: Wed,  1 Jul 2020 16:04:06 +0800
Message-ID: <20200701080411.5802-7-weijiang.yang@intel.com> (raw)
In-Reply-To: <20200701080411.5802-1-weijiang.yang@intel.com>

From: Sean Christopherson <sean.j.christopherson@intel.com>

A handful of CET MSRs are not context switched through "traditional"
methods, e.g. VMCS or manual switching, but rather are passed through
to the guest and are saved and restored by XSAVES/XRSTORS, i.e. in the
guest's FPU state.

Load the guest's FPU state if userspace is accessing MSRs whose values
are managed by XSAVES so that the MSR helper, e.g. vmx_{get,set}_msr(),
can simply do {RD,WR}MSR to access the guest's value.

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

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Co-developed-by: Yang Weijiang <weijiang.yang@intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
 arch/x86/kvm/x86.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c866087ed0ef..50f80dcab3a9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -109,6 +109,8 @@ static void enter_smm(struct kvm_vcpu *vcpu);
 static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);
 static void store_regs(struct kvm_vcpu *vcpu);
 static int sync_regs(struct kvm_vcpu *vcpu);
+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;
@@ -3267,6 +3269,12 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
+static bool is_xsaves_msr(u32 index)
+	return index == MSR_IA32_U_CET ||
+	       (index >= MSR_IA32_PL0_SSP && index <= MSR_IA32_PL3_SSP);
  * Read or write a bunch of msrs. All parameters are kernel addresses.
@@ -3277,11 +3285,20 @@ 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 && supported_xss &&
+		    is_xsaves_msr(entries[i].index)) {
+			kvm_load_guest_fpu(vcpu);
+			fpu_loaded = true;
+		}
 		if (do_msr(vcpu, entries[i].index, &entries[i].data))
+	}
+	if (fpu_loaded)
+		kvm_put_guest_fpu(vcpu);
 	return i;

  parent reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-01  8:04 [PATCH v13 00/11] Introduce support for guest CET feature Yang Weijiang
2020-07-01  8:04 ` [PATCH v13 01/11] KVM: x86: Include CET definitions for KVM test purpose Yang Weijiang
2020-07-01  8:04 ` [PATCH v13 02/11] KVM: VMX: Introduce CET VMCS fields and flags Yang Weijiang
2020-07-01  8:04 ` [PATCH v13 03/11] KVM: VMX: Set guest CET MSRs per KVM and host configuration Yang Weijiang
2020-07-02 15:13   ` Xiaoyao Li
2020-07-03 15:02     ` Yang Weijiang
2020-07-01  8:04 ` [PATCH v13 04/11] KVM: VMX: Configure CET settings upon guest CR0/4 changing Yang Weijiang
2020-07-01  8:04 ` [PATCH v13 05/11] KVM: x86: Refresh CPUID once guest changes XSS bits Yang Weijiang
2020-07-01  8:04 ` Yang Weijiang [this message]
2020-07-01  8:04 ` [PATCH v13 07/11] KVM: x86: Add userspace access interface for CET MSRs Yang Weijiang
2020-07-01  8:04 ` [PATCH v13 08/11] KVM: VMX: Enable CET support for nested VM Yang Weijiang
2020-07-01  8:04 ` [PATCH v13 09/11] KVM: VMX: Add VMCS dump and sanity check for CET states Yang Weijiang
2020-07-01  8:04 ` [PATCH v13 10/11] KVM: x86: Add #CP support in guest exception dispatch Yang Weijiang
2020-07-01  8:04 ` [PATCH v13 11/11] KVM: x86: Enable CET virtualization and advertise CET to userspace Yang Weijiang

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