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remove the outdated comments and local_irq_save()/local_irq_restore()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.
> 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
> >
> >
