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 5a1faf3f043e37b780a5b25f8f89c51d9b3954b9..f4a555beef1908b78c9ad6992d4727d59d9c81ee 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 59b69f6a2844cdce101a69c3bb34eb7ccd30556f..1d08ad3582d07fd61cd03302eba547e3a997058b 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 c3b1ad9fca818befb9e5920f7eb7c0d2b703d245..496b3695d3d3c96fd2687b2b6bc013d9ee8d96e5 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 5f3818846465caa1b87f4a7afafec62ad8a02b89..ea306adbbc13603591d46d3f062cc20cf1bc37d1 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)