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>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5a1faf3..f4a555b 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -401,6 +401,7 @@ struct kvm_vcpu_arch {
        struct kvm_mmu_memory_cache mmu_page_header_cache;
 
        struct fpu guest_fpu;
+       bool eager_fpu;
        u64 xcr0;
        u64 guest_supported_xcr0;
        u32 guest_xstate_size;

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 59b69f6..1d08ad3 100644 (file)
--- 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 c3b1ad9..496b369 100644 (file)
--- 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 5f38188..ea306ad 100644 (file)
--- 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)