From e10a73f5380958629b4ae8d2ecad29f3e82a1b7f Mon Sep 17 00:00:00 2001 From: Rishabh Bhatnagar Date: Wed, 10 May 2023 18:15:43 +0000 Subject: [PATCH] KVM: x86: do not set st->preempted when going back to user space From: Paolo Bonzini commit 54aa83c90198e68eee8b0850c749bc70efb548da upstream. Similar to the Xen path, only change the vCPU's reported state if the vCPU was actually preempted. The reason for KVM's behavior is that for example optimistic spinning might not be a good idea if the guest is doing repeated exits to userspace; however, it is confusing and unlikely to make a difference, because well-tuned guests will hardly ever exit KVM_RUN in the first place. Suggested-by: Sean Christopherson Signed-off-by: Paolo Bonzini [risbhat@amazon.com: Don't check for xen msr as support is not available and skip the SEV-ES condition] Signed-off-by: Rishabh Bhatnagar Tested-by: Allen Pais Acked-by: Sean Christopherson Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/x86.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 3881bf7d1ac4..116a225fb26e 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4139,16 +4139,18 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) { int idx; - if (vcpu->preempted) + if (vcpu->preempted) { vcpu->arch.preempted_in_kernel = !kvm_x86_ops.get_cpl(vcpu); - /* - * kvm_memslots() will be called by - * kvm_write_guest_offset_cached() so take the srcu lock. - */ - idx = srcu_read_lock(&vcpu->kvm->srcu); - kvm_steal_time_set_preempted(vcpu); - srcu_read_unlock(&vcpu->kvm->srcu, idx); + /* + * Take the srcu lock as memslots will be accessed to check the gfn + * cache generation against the memslots generation. + */ + idx = srcu_read_lock(&vcpu->kvm->srcu); + kvm_steal_time_set_preempted(vcpu); + srcu_read_unlock(&vcpu->kvm->srcu, idx); + } + kvm_x86_ops.vcpu_put(vcpu); vcpu->arch.last_host_tsc = rdtsc(); /*