[PATCH] RISC-V: KVM: Use a raw lock for IMSIC wakeup state

[Anup Patel]

On Fri, Oct 9, 2026 at 3:44 PM Andrew Jones
<andrew.jones at oss.qualcomm.com> wrote:
>
> Hi Anup,
>
> On Fri, Oct 09, 2026 at 01:45:20PM +0200, Anup Patel wrote:
> > On Fri, Sep 25, 2026 at 5:51 PM Andrew Jones
> > <andrew.jones at oss.qualcomm.com> wrote:
> > >
> > > kvm_riscv_vcpu_aia_imsic_put() can run from the scheduler preemption
> > > notifier while the raw runqueue lock is held. Taking vsfile_lock, an
> > > rwlock_t, there violates the lockdep wait-context rules.
> > >
> > > Protect the CPU/HGEI pair with a separate raw spinlock. All updates to
> > > that pair retain vsfile_lock and take the new lock, while scheduler-out
> > > uses only the new lock around the HGEIE update. This keeps the wakeup
> > > setup serialized with VS-file publication and release without bringing
> > > wider IMSIC operations into a raw critical section.
> >
> > Instead of introducing another lock, why not replace
> > read_lock_irqsave(&imsic->vsfile_lock, flags) with
> > write_lock_irqsave(&imsic->vsfile_lock, flags) in
> > kvm_riscv_vcpu_aia_imsic_put() ??
>
> Unfortunately, write_lock_irqsave() has the same PREEMPT_RT issue, since
> rwlock_t is sleepable on RT in both modes.
>

I am not fond of nested locking, why not convert vsfile_lock into raw
spinlock ??

Regards,
Anup