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KVM: x86: Handle TIF_NEED_FPU_LOAD in kvm_{load,put}_guest_fpu() 

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: 5f409e20b7 ("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>
This commit is contained in:
Sean Christopherson 2020-01-17 11:30:49 -08:00 committed by Paolo Bonzini
parent 3911b65ee1
commit c9aef3b85f
1 changed files with 17 additions and 2 deletions
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19
arch/x86/kvm/x86.c
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@ -8558,12 +8558,26 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
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);
@ -8579,7 +8593,8 @@ static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
{
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();