| Message ID | 20240522014013.1672962-2-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: Fold kvm_arch_sched_in() into kvm_arch_vcpu_load() | expand |
On Tue, May 21, 2024 at 06:40:08PM -0700, Sean Christopherson wrote: > Add a kvm_vcpu.scheduled_out flag to track if a vCPU is in the process of > being scheduled out (vCPU put path), or if the vCPU is being reloaded > after being scheduled out (vCPU load path). In the short term, this will > allow dropping kvm_arch_sched_in(), as arch code can query scheduled_out > during kvm_arch_vcpu_load(). > > Longer term, scheduled_out opens up other potential optimizations, without > creating subtle/brittle dependencies. E.g. it allows KVM to keep guest > state (that is managed via kvm_arch_vcpu_{load,put}()) loaded across > kvm_sched_{out,in}(), if KVM knows the state isn't accessed by the host > kernel. Forcing arch code to coordinate between kvm_arch_sched_{in,out}() > and kvm_arch_vcpu_{load,put}() is awkward, not reusable, and relies on the > exact ordering of calls into arch code. > > Adding scheduled_out also obviates the need for a kvm_arch_sched_out() > hook, e.g. if arch code needs to do something novel when putting vCPU > state. > > And even if KVM never uses scheduled_out for anything beyond dropping > kvm_arch_sched_in(), just being able to remove all of the arch stubs makes > it worth adding the flag. > > Link: https://lore.kernel.org/all/20240430224431.490139-1-seanjc@google.com > Cc: Oliver Upton <oliver.upton@linux.dev> > Signed-off-by: Sean Christopherson <seanjc@google.com> Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 7b57878c8c18..bde69f74b031 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -380,6 +380,7 @@ struct kvm_vcpu { #endif bool preempted; bool ready; + bool scheduled_out; struct kvm_vcpu_arch arch; struct kvm_vcpu_stat stat; char stats_id[KVM_STATS_NAME_SIZE]; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index a1756d5077ee..7ecea573d121 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -6288,6 +6288,8 @@ static void kvm_sched_in(struct preempt_notifier *pn, int cpu) __this_cpu_write(kvm_running_vcpu, vcpu); kvm_arch_sched_in(vcpu, cpu); kvm_arch_vcpu_load(vcpu, cpu); + + WRITE_ONCE(vcpu->scheduled_out, false); } static void kvm_sched_out(struct preempt_notifier *pn, @@ -6295,6 +6297,8 @@ static void kvm_sched_out(struct preempt_notifier *pn, { struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn); + WRITE_ONCE(vcpu->scheduled_out, true); + if (current->on_rq) { WRITE_ONCE(vcpu->preempted, true); WRITE_ONCE(vcpu->ready, true);
Add a kvm_vcpu.scheduled_out flag to track if a vCPU is in the process of being scheduled out (vCPU put path), or if the vCPU is being reloaded after being scheduled out (vCPU load path). In the short term, this will allow dropping kvm_arch_sched_in(), as arch code can query scheduled_out during kvm_arch_vcpu_load(). Longer term, scheduled_out opens up other potential optimizations, without creating subtle/brittle dependencies. E.g. it allows KVM to keep guest state (that is managed via kvm_arch_vcpu_{load,put}()) loaded across kvm_sched_{out,in}(), if KVM knows the state isn't accessed by the host kernel. Forcing arch code to coordinate between kvm_arch_sched_{in,out}() and kvm_arch_vcpu_{load,put}() is awkward, not reusable, and relies on the exact ordering of calls into arch code. Adding scheduled_out also obviates the need for a kvm_arch_sched_out() hook, e.g. if arch code needs to do something novel when putting vCPU state. And even if KVM never uses scheduled_out for anything beyond dropping kvm_arch_sched_in(), just being able to remove all of the arch stubs makes it worth adding the flag. Link: https://lore.kernel.org/all/20240430224431.490139-1-seanjc@google.com Cc: Oliver Upton <oliver.upton@linux.dev> Signed-off-by: Sean Christopherson <seanjc@google.com> --- include/linux/kvm_host.h | 1 + virt/kvm/kvm_main.c | 4 ++++ 2 files changed, 5 insertions(+)