On Tue, 21 Jan 2025 08:05:57 -0800
Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> On Mon, Jan 20, 2025, Christoph Schlameuss wrote:
> > On Sat Jan 11, 2025 at 1:20 AM CET, Sean Christopherson wrote:
> > > Add a dedicated API for setting internal memslots, and have it explicitly
> > > disallow setting userspace memslots. Setting a userspace memslots without
> > > a direct command from userspace would result in all manner of issues.
> > >
> > > No functional change intended.
> > >
> > > Cc: Tao Su <tao1.su@xxxxxxxxxxxxxxx>
> > > Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
> > > Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > > ---
> > > arch/x86/kvm/x86.c | 2 +-
> > > include/linux/kvm_host.h | 4 ++--
> > > virt/kvm/kvm_main.c | 15 ++++++++++++---
> > > 3 files changed, 15 insertions(+), 6 deletions(-)
> >
> > [...]
> >
> > > +int kvm_set_internal_memslot(struct kvm *kvm,
> > > + const struct kvm_userspace_memory_region2 *mem)
> > > +{
> > > + if (WARN_ON_ONCE(mem->slot < KVM_USER_MEM_SLOTS))
> > > + return -EINVAL;
> > > +
> >
> > Looking at Claudios changes I found that this is missing to acquire the
> > slots_lock here.
> >
> > guard(mutex)(&kvm->slots_lock);
>
> It's not missing. As of this patch, x86 is the only user of KVM-internal memslots,
> and x86 acquires slots_lock outside of kvm_set_internal_memslot() because x86 can
> have multiple address spaces (regular vs SMM) and KVM's internal memslots need to
> be created for both, i.e. it's desirable to holds slots_lock in the caller.
>
> If it's annoying for s390 to acquire slots_lock, we could add a wrapper, i.e. turn
> this into __kvm_set_internal_memslot() and then re-add kvm_set_internal_memslot()
> as a version that acquires and releases slots_lock.
I think it's fine as it is, just document that the lock needs to be
held
I'll add the necessary locking in the s390 code
