kvm/fpu: Enable eager restore kvm FPU for MPX

The MPX feature requires eager KVM FPU restore support. We have verified
that MPX cannot work correctly with the current lazy KVM FPU restore
mechanism. Eager KVM FPU restore should be enabled if the MPX feature is
exposed to VM.

Signed-off-by: Yang Zhang <yang.z.zhang@intel.com>
Signed-off-by: Liang Li <liang.z.li@intel.com>
[Also activate the FPU on AMD processors. - Paolo]
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 26 insertions, 2 deletions

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 59b69f6a2844..1d08ad3582d0 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -16,6 +16,8 @@
 #include <linux/module.h>
 #include <linux/vmalloc.h>
 #include <linux/uaccess.h>
+#include <asm/i387.h> /* For use_eager_fpu.  Ugh! */
+#include <asm/fpu-internal.h> /* For use_eager_fpu.  Ugh! */
 #include <asm/user.h>
 #include <asm/xsave.h>
 #include "cpuid.h"
@@ -95,6 +97,8 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
         if (best && (best->eax & (F(XSAVES) | F(XSAVEC))))
                 best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
 
+        vcpu->arch.eager_fpu = guest_cpuid_has_mpx(vcpu);
+
         /*
          * The existing code assumes virtual address is 48-bit in the canonical
          * address checks; exit if it is ever changed.
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index c3b1ad9fca81..496b3695d3d3 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -117,4 +117,12 @@ static inline bool guest_cpuid_has_rtm(struct kvm_vcpu *vcpu)
         best = kvm_find_cpuid_entry(vcpu, 7, 0);
         return best && (best->ebx & bit(X86_FEATURE_RTM));
 }
+
+static inline bool guest_cpuid_has_mpx(struct kvm_vcpu *vcpu)
+{
+        struct kvm_cpuid_entry2 *best;
+
+        best = kvm_find_cpuid_entry(vcpu, 7, 0);
+        return best && (best->ebx & bit(X86_FEATURE_MPX));
+}
 #endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5f3818846465..ea306adbbc13 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7060,7 +7060,9 @@ void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
         fpu_save_init(&vcpu->arch.guest_fpu);
         __kernel_fpu_end();
         ++vcpu->stat.fpu_reload;
-        kvm_make_request(KVM_REQ_DEACTIVATE_FPU, vcpu);
+        if (!vcpu->arch.eager_fpu)
+                kvm_make_request(KVM_REQ_DEACTIVATE_FPU, vcpu);
+
         trace_kvm_fpu(0);
 }
 
@@ -7076,11 +7078,21 @@ void kvm_arch_vcpu_free(struct kvm_vcpu *vcpu)
 struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
                                                 unsigned int id)
 {
+        struct kvm_vcpu *vcpu;
+
         if (check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0)
                 printk_once(KERN_WARNING
                 "kvm: SMP vm created on host with unstable TSC; "
                 "guest TSC will not be reliable\n");
-        return kvm_x86_ops->vcpu_create(kvm, id);
+
+        vcpu = kvm_x86_ops->vcpu_create(kvm, id);
+
+        /*
+         * Activate fpu unconditionally in case the guest needs eager FPU.  It will be
+         * deactivated soon if it doesn't.
+         */
+        kvm_x86_ops->fpu_activate(vcpu);
+        return vcpu;
 }
 
 int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)