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* [PATCH] KVM: x86: move saving of arch.host_pkru to kvm_arch_vcpu_load in 5.4.y
@ 2021-05-06 17:02 Jon Kohler
  0 siblings, 0 replies; only message in thread
From: Jon Kohler @ 2021-05-06 17:02 UTC (permalink / raw)
  Cc: Jon Kohler, stable, Babu Moger, Paolo Bonzini,
	Radim Krčmář,
	Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
	Joerg Roedel, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
	H. Peter Anvin, x86, kvm, linux-kernel

commit 37486135d3a7b03acc7755b63627a130437f066a upstream.

In 5.4.y only, vcpu->arch.host_pkru is being set on every run thru
of vcpu_enter_guest, when it really only needs to be set on load. As
a result, we're doing a rdpkru on supported CPUs on every iteration
of vcpu_enter_guest even though the value never changes.

Mainline and 5.10.y already has host_pkru being initialized in
kvm_arch_vcpu_load. This change is 5.4.y specific and moves
host_pkru save to kvm_arch_vcpu_load.

Fixes: 99e392a4979b ("KVM: x86: Fix pkru save/restore when guest CR4.PKE=0, move it to x86.c")
Cc: stable@vger.kernel.org # 5.4.y
Cc: Babu Moger <babu.moger@amd.com>
Signed-off-by: Jon Kohler <jon@nutanix.com>
---
 arch/x86/kvm/x86.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 153659e8f403..1f7521752a94 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3507,6 +3507,9 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 
 	kvm_x86_ops->vcpu_load(vcpu, cpu);
 
+	/* Save host pkru register if supported */
+	vcpu->arch.host_pkru = read_pkru();
+
 	/* Apply any externally detected TSC adjustments (due to suspend) */
 	if (unlikely(vcpu->arch.tsc_offset_adjustment)) {
 		adjust_tsc_offset_host(vcpu, vcpu->arch.tsc_offset_adjustment);
@@ -8253,9 +8256,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	trace_kvm_entry(vcpu->vcpu_id);
 	guest_enter_irqoff();
 
-	/* Save host pkru register if supported */
-	vcpu->arch.host_pkru = read_pkru();
-
 	fpregs_assert_state_consistent();
 	if (test_thread_flag(TIF_NEED_FPU_LOAD))
 		switch_fpu_return();
-- 
2.30.1 (Apple Git-130)


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