Re: [PATCH] RISC-V: KVM: Fix TOCTOU race in SBI system suspend handler

On Fri, May 22, 2026 at 03:18:13AM +0000, Jiakai Xu wrote:
> Hi, drew!
> 
> Thanks for your review!
> 
> > > I'm not a big fan of this approach and I see sashiko found it has gaps[1].
> 
> I read sashiko's feedback and I think it makes sense.
> 
> > > I'd rather we introduce a mutex to kvm_arch to serialize cross-vcpu
> > 
> > Eh, not sure why I said 'introduce' here. We can just use kvm->lock.
> 
> I looked into that, but it may be not suitable. Here's why:
> 
> Documentation/virt/kvm/locking.rst explicitly states: kvm->lock is taken 
> outside vcpu->mutex. The susp handler runs inside kvm_arch_vcpu_ioctl_run(), 
> which is called from kvm_vcpu_ioctl() where vcpu->mutex is already held.
> 
> Taking kvm->lock inside the susp handler would produce: vcpu->mutex → kvm->lock.
> So may be we should introduce a mutex to kvm_arch to serialize cross-vcpu
> mp-state operations.
> 
> What do you think?

Good catch. I should have trusted my initial instincts to introduce a new
mutex :-)

Thanks,
drew

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