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Subject[PATCH 2/2] KVM: x86: Skip zeroing of MPX state on reset event
Date
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@intel.com>
---
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) {
--
2.24.0
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