On Fri 22-06-18 09:42:57, Michal Hocko wrote:
> On Thu 21-06-18 13:50:53, David Rientjes wrote:
> > On Thu, 21 Jun 2018, Michal Hocko wrote:
> >
> > > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > > > index 6bcecc325e7e..ac08f5d711be 100644
> > > > > --- a/arch/x86/kvm/x86.c
> > > > > +++ b/arch/x86/kvm/x86.c
> > > > > @@ -7203,8 +7203,9 @@ static void vcpu_load_eoi_exitmap(struct kvm_vcpu *vcpu)
> > > > > kvm_x86_ops->load_eoi_exitmap(vcpu, eoi_exit_bitmap);
> > > > > }
> > > > >
> > > > > -void kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
> > > > > - unsigned long start, unsigned long end)
> > > > > +int kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
> > > > > + unsigned long start, unsigned long end,
> > > > > + bool blockable)
> > > > > {
> > > > > unsigned long apic_address;
> > > > >
> > > > > @@ -7215,6 +7216,8 @@ void kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
> > > > > apic_address = gfn_to_hva(kvm, APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
> > > > > if (start <= apic_address && apic_address < end)
> > > > > kvm_make_all_cpus_request(kvm, KVM_REQ_APIC_PAGE_RELOAD);
> > > > > +
> > > > > + return 0;
> > > > > }
> > > > >
> > > > > void kvm_vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu)
> > > >
> > > > Auditing the first change in the patch, this is incorrect because
> > > > kvm_make_all_cpus_request() for KVM_REQ_APIC_PAGE_RELOAD can block in
> > > > kvm_kick_many_cpus() and that is after kvm_make_request() has been done.
> > >
> > > I would have to check the code closer. But doesn't
> > > kvm_make_all_cpus_request call get_cpu which is preempt_disable? I
> > > definitely plan to talk to respective maintainers about these changes of
> > > course.
> > >
> >
> > preempt_disable() is required because it calls kvm_kick_many_cpus() with
> > wait == true because KVM_REQ_APIC_PAGE_RELOAD sets KVM_REQUEST_WAIT and
> > thus the smp_call_function_many() is going to block until all cpus can run
> > ack_flush().
>
> I will make sure to talk to the maintainer of the respective code to
> do the nonblock case correctly.
I've just double checked this particular code and the wait path and this
one is not a sleep. It is a busy wait for IPI to get handled. So this
one should be OK AFAICS. Anyway I will send an RFC and involve
respective maintainers to make sure I am not making any incorrect
assumptions.
--
Michal Hocko
SUSE Labs
