KVM: x86: Don't disable IRQs when unregistering user-return notifier

Remove the code to disable IRQs when unregistering KVM's user-return
notifier now that KVM doesn't invoke kvm_on_user_return() when disabling
virtualization via IPI function call, i.e. now that there's no need to
guard against re-entrancy via IPI callback.

Note, disabling IRQs has largely been unnecessary since commit
a377ac1cd9d7b ("x86/entry: Move user return notifier out of loop") moved
fire_user_return_notifiers() into the section with IRQs disabled.  In doing
so, the commit somewhat inadvertently fixed the underlying issue that
was papered over by commit 1650b4ebc99d ("KVM: Disable irq while
unregistering user notifier").  I.e. in practice, the code and comment
has been stale since commit a377ac1cd9d7b.

Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
[sean: rewrite changelog after rebasing, drop lockdep assert]
Reviewed-by: Kai Huang <kai.huang@intel.com>
Link: https://patch.msgid.link/20251030191528.3380553-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3bc3d527f442aae69c618236cfdeb118599c104a..97852f190720a539e2651a2f946c6840a43745e2 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -602,18 +602,10 @@ 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);
+       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) {