On 09/12/19 21:19, Sean Christopherson wrote:
> Don't bother zeroing out MPX state in the guest's FPU on a reset event,
> the guest's FPU is always zero allocated and there is no path between
> kvm_arch_vcpu_create() and kvm_arch_vcpu_setup() that can lead to guest
> MPX state being modified.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Makes sense, but it's a bit weird to have INIT reset _less_ state than
RESET... I've queued patch 1 only for now.
Paolo
> ---
> arch/x86/kvm/x86.c | 12 +++++-------
> 1 file changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 854ae27bb021..e6f4174f55cd 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9194,15 +9194,14 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> kvm_async_pf_hash_reset(vcpu);
> vcpu->arch.apf.halted = false;
>
> - if (kvm_mpx_supported()) {
> + if (kvm_mpx_supported() && init_event) {
> void *mpx_state_buffer;
>
> /*
> - * To avoid have the INIT path from kvm_apic_has_events() that be
> - * called with loaded FPU and does not let userspace fix the state.
> + * Temporarily flush the guest's FPU to memory so that zeroing
> + * out the MPX areas is done using up-to-date state.
> */
> - if (init_event)
> - kvm_put_guest_fpu(vcpu);
> + kvm_put_guest_fpu(vcpu);
> mpx_state_buffer = get_xsave_addr(&vcpu->arch.guest_fpu->state.xsave,
> XFEATURE_BNDREGS);
> if (mpx_state_buffer)
> @@ -9211,8 +9210,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> XFEATURE_BNDCSR);
> if (mpx_state_buffer)
> memset(mpx_state_buffer, 0, sizeof(struct mpx_bndcsr));
> - if (init_event)
> - kvm_load_guest_fpu(vcpu);
> + kvm_load_guest_fpu(vcpu);
> }
>
> if (!init_event) {
>
