Revert "kvm: x86: Use task structs fpu field for user"

commit ec269475 upstream.

This reverts commit 240c35a3
("kvm: x86: Use task structs fpu field for user", 2018-11-06).
The commit is broken and causes QEMU's FPU state to be destroyed
when KVM_RUN is preempted.

Fixes: 240c35a3 ("kvm: x86: Use task structs fpu field for user")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/include/asm/kvm_host.h

@@ -609,15 +609,16 @@ struct kvm_vcpu_arch {
 
 	/*
 	 * QEMU userspace and the guest each have their own FPU state.
-	 * In vcpu_run, we switch between the user, maintained in the
-	 * task_struct struct, and guest FPU contexts. While running a VCPU,
-	 * the VCPU thread will have the guest FPU context.
+	 * In vcpu_run, we switch between the user and guest FPU contexts.
+	 * While running a VCPU, the VCPU thread will have the guest FPU
+	 * context.
 	 *
 	 * Note that while the PKRU state lives inside the fpu registers,
 	 * it is switched out separately at VMENTER and VMEXIT time. The
 	 * "guest_fpu" state here contains the guest FPU context, with the
 	 * host PRKU bits.
 	 */
+	struct fpu user_fpu;
 	struct fpu *guest_fpu;
 
 	u64 xcr0;

arch/x86/kvm/x86.c

@@ -8172,7 +8172,7 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
 static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
 {
 	preempt_disable();
-	copy_fpregs_to_fpstate(&current->thread.fpu);
+	copy_fpregs_to_fpstate(&vcpu->arch.user_fpu);
 	/* PKRU is separately restored in kvm_x86_ops->run.  */
 	__copy_kernel_to_fpregs(&vcpu->arch.guest_fpu->state,
 				~XFEATURE_MASK_PKRU);
@@ -8185,7 +8185,7 @@ static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
 {
 	preempt_disable();
 	copy_fpregs_to_fpstate(vcpu->arch.guest_fpu);
-	copy_kernel_to_fpregs(&current->thread.fpu.state);
+	copy_kernel_to_fpregs(&vcpu->arch.user_fpu.state);
 	preempt_enable();
 	++vcpu->stat.fpu_reload;
 	trace_kvm_fpu(0);