On Mon, Dec 02, 2019 at 11:30:27AM -0800, Sean Christopherson wrote: > On Fri, Nov 29, 2019 at 04:34:53PM -0500, Peter Xu wrote: > > It's already going to reach 2400 Bytes (which is over half of page > > size on 4K page archs), so maybe it's good to have this build-time > > check in case it overflows when adding new fields. > > Please explain why exceeding PAGE_SIZE is a bad thing. I realize it's > almost absurdly obvious when looking at the code, but a) the patch itself > does not provide that context and b) the changelog should hold up on its > own, Right, I'll enhance the commit message. > e.g. in a mostly hypothetical case where the allocation of vcpu->run > were changed to something else. And that's why I added BUILD_BUG_ON right beneath that allocation. :) It's just a helper for developers when adding new kvm_run fields, not a risk for anyone who wants to start allocating more pages for it. Thanks, > > > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> > > --- > > virt/kvm/kvm_main.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > index 8f8940cc4b84..681452d288cd 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -352,6 +352,8 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id) > > } > > vcpu->run = page_address(page); > > > > + BUILD_BUG_ON(sizeof(struct kvm_run) > PAGE_SIZE); > > + > > kvm_vcpu_set_in_spin_loop(vcpu, false); > > kvm_vcpu_set_dy_eligible(vcpu, false); > > vcpu->preempted = false; > > -- > > 2.21.0 > > > -- Peter Xu
