[PATCH 5.5 255/367] KVM: x86: Handle TIF_NEED_FPU_LOAD in kvm_{load,put}_guest_fpu()

Greg Kroah-Hartman
2020-02-10T12:46:08Z

From: Sean Christopherson <sean.j.christopherson@intel.com>

commit c9aef3b85f425d1f6635382ec210ee5a7ef55d7d upstream.

Handle TIF_NEED_FPU_LOAD similar to how fpu__copy() handles the flag
when duplicating FPU state to a new task struct. TIF_NEED_FPU_LOAD can
be set any time control is transferred out of KVM, be it voluntarily,
e.g. if I/O is triggered during a KVM call to get_user_pages, or
involuntarily, e.g. if softirq runs after an IRQ occurs. Therefore,
KVM must account for TIF_NEED_FPU_LOAD whenever it is (potentially)
accessing CPU FPU state.

Fixes: 5f409e20b7945 ("x86/fpu: Defer FPU state load until return to userspace")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/x86.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8517,12 +8517,26 @@ static int complete_emulated_mmio(struct
return 0;
}

+static void kvm_save_current_fpu(struct fpu *fpu)
+{
+ /*
+ * If the target FPU state is not resident in the CPU registers, just
+ * memcpy() from current, else save CPU state directly to the target.
+ */
+ if (test_thread_flag(TIF_NEED_FPU_LOAD))
+ memcpy(&fpu->state, &current->thread.fpu.state,
+ fpu_kernel_xstate_size);
+ else
+ copy_fpregs_to_fpstate(fpu);
+}
+
/* Swap (qemu) user FPU context for the guest FPU context. */
static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
{
fpregs_lock();

- copy_fpregs_to_fpstate(vcpu->arch.user_fpu);
+ kvm_save_current_fpu(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);
@@ -8538,7 +8552,8 @@ static void kvm_put_guest_fpu(struct kvm
{
fpregs_lock();

- copy_fpregs_to_fpstate(vcpu->arch.guest_fpu);
+ kvm_save_current_fpu(vcpu->arch.guest_fpu);
+
copy_kernel_to_fpregs(&vcpu->arch.user_fpu->state);

fpregs_mark_activate();