KVM: Initialize fpu state in preemptible context

init_fpu() (which is indirectly called by the fpu switching code) assumes
it is in process context.  Rather than makeing init_fpu() use an atomic
allocation, which can cause a task to be killed, make sure the fpu is
already initialized when we enter the run loop.

KVM-Stable-Tag.
Reported-and-tested-by: Kirill A. Shutemov <kas@openvz.org>
Acked-by: Pekka Enberg <penberg@kernel.org>
Reviewed-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fa708c9a7437..9dda70dffac1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5376,6 +5376,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
         int r;
         sigset_t sigsaved;
 
+        if (!tsk_used_math(current) && init_fpu(current))
+                return -ENOMEM;
+
         if (vcpu->sigset_active)
                 sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved);