Re: [PATCH v1 02/11] KVM: s390: Use srcu in kvm_arch_vcpu_unlocked_ioctl()

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Tue, 11 Aug 2026 19:26:42 +0200
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> Am 11.08.26 um 17:56 schrieb Claudio Imbrenda:
> > kvm_arch_vcpu_unlocked_ioctl() is called without further locks held, but
> > kvm_s390_inject_vcpu(), which is called from there, needs either the
> > kvm->srcu or the slots lock.
> > 
> > Fix by taking the kvm->srcu in kvm_arch_vcpu_unlocked_ioctl().
> > 
> > Fixes: ba5c1e9b6cee ("KVM: s390: interrupt subsystem, cpu timer, waitpsw")
> > Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> > ---
> >   arch/s390/kvm/kvm-s390.c | 2 ++
> >   1 file changed, 2 insertions(+)
> > 
> > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> > index 518a69c55e85..02c5428ba239 100644
> > --- a/arch/s390/kvm/kvm-s390.c
> > +++ b/arch/s390/kvm/kvm-s390.c
> > @@ -5444,6 +5444,8 @@ long kvm_arch_vcpu_unlocked_ioctl(struct file *filp, unsigned int ioctl,
> >   	void __user *argp = (void __user *)arg;
> >   	int rc;
> >   
> > +	guard(srcu)(&vcpu->kvm->srcu);
> > +  
> 
> not a bug, but just having srcu around both inject would avoid having holding srcu on the
> argument usercopy. This is not forbidden but might just take a while when paging.
> 
>   scoped_guard(srcu)(&vcpu->kvm->srcu)
>                        rc = kvm_s390_inject_vcpu(vcpu, &s390irq);
> 
> in any way, no objection to your variant and a real fix.
> 
> Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>

I had not considered the user copy; I will definitely respin with the
scoped_guard()

> 
> 
> >   	switch (ioctl) {
> >   	case KVM_S390_IRQ: {
> >   		struct kvm_s390_irq s390irq;  
>