On Fri, Sep 12, 2025 at 05:38:22PM +0800, Hou Wenlong wrote:
> On Fri, Sep 12, 2025 at 04:35:00PM +0800, Chao Gao wrote:
> > On Fri, Sep 12, 2025 at 03:35:29PM +0800, Hou Wenlong wrote:
> > >The commit a377ac1cd9d7b ("x86/entry: Move user return notifier out of
> > >loop") moved fire_user_return_notifiers() into the section with
> > >interrupts disabled, so the callback kvm_on_user_return() cannot be
> > >interrupted by kvm_arch_disable_virtualization_cpu() now. Therefore,
> > >remove the outdated comments and local_irq_save()/local_irq_restore()
> > >code in kvm_on_user_return().
> > >
> > >Signed-off-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
> > >---
> > > arch/x86/kvm/x86.c | 16 +++++-----------
> > > 1 file changed, 5 insertions(+), 11 deletions(-)
> > >
> > >diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > >index 33fba801b205..10afbacb1851 100644
> > >--- a/arch/x86/kvm/x86.c
> > >+++ b/arch/x86/kvm/x86.c
> > >@@ -568,18 +568,12 @@ static void kvm_on_user_return(struct user_return_notifier *urn)
> > > struct kvm_user_return_msrs *msrs
> > > = container_of(urn, struct kvm_user_return_msrs, urn);
> > > struct kvm_user_return_msr_values *values;
> > >- unsigned long flags;
> > >
> > >- /*
> > >- * Disabling irqs at this point since the following code could be
> > >- * interrupted and executed through kvm_arch_disable_virtualization_cpu()
> > >- */
> > >- local_irq_save(flags);
> > >- if (msrs->registered) {
> > >- msrs->registered = false;
> > >- user_return_notifier_unregister(urn);
> > >- }
> > >- local_irq_restore(flags);
> > >+ lockdep_assert_irqs_disabled();
> >
> > kvm_offline_cpu() may call into this function. But I am not sure if interrupts
> > are disabled in that path.
> >
> Thanks for pointing that out. I see that interrupts are enabled in the
> callback during the CPU offline test. I'll remove the
> lockdep_assert_irqs_disabled() here.
>
Upon a second look, can we just disable interrupts in kvm_cpu_offline()?
The other paths that call kvm_disable_virtualization_cpu() are all in an
interrupt-disabled state, although it seems that
kvm_disable_virtualization_cpu() cannot be reentered.
> > Documentation/core-api/cpu_hotplug.rst says that callbacks in the ONLINE section
> > are invoked with interrupts and preemption enabled.
> >
> > >+
> > >+ msrs->registered = false;
> > >+ user_return_notifier_unregister(urn);
> > >+
> > > for (slot = 0; slot < kvm_nr_uret_msrs; ++slot) {
> > > values = &msrs->values[slot];
> > > if (values->host != values->curr) {
> > >--
> > >2.31.1
> > >
> > >
