On Tue, Jul 25, 2023, Yu Zhang wrote: > On Fri, Jul 21, 2023 at 06:23:48PM -0700, Sean Christopherson wrote: > > Explicitly check that tdp_iter_start() is handed a valid shadow page > > to harden KVM against bugs where > > Sorry, where? Gah, I must have seen something shiny when writing the changelog. > It's not about guest using an invisible GFN, it's about a KVM bug, right? Yes, the intent is to guard against a KVM bug, e.g. if KVM managed to get into the TDP MMU with an invalid root, or a root belonging to a shadow MMU. I'll fix the changelog in v2. > > Opportunistically stop the TDP MMU iteration instead of continuing on > > with garbage if the incoming root is bogus. Attempting to walk a garbage > > root is more likely to caused major problems than doing nothing. > > > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > > --- > > arch/x86/kvm/mmu/tdp_iter.c | 11 ++++++----- > > 1 file changed, 6 insertions(+), 5 deletions(-) > > > > diff --git a/arch/x86/kvm/mmu/tdp_iter.c b/arch/x86/kvm/mmu/tdp_iter.c > > index d2eb0d4f8710..bd30ebfb2f2c 100644 > > --- a/arch/x86/kvm/mmu/tdp_iter.c > > +++ b/arch/x86/kvm/mmu/tdp_iter.c > > @@ -39,13 +39,14 @@ void tdp_iter_restart(struct tdp_iter *iter) > > void tdp_iter_start(struct tdp_iter *iter, struct kvm_mmu_page *root, > > int min_level, gfn_t next_last_level_gfn) > > { > > - int root_level = root->role.level; > > - > > - WARN_ON(root_level < 1); > > - WARN_ON(root_level > PT64_ROOT_MAX_LEVEL); > > + if (WARN_ON_ONCE(!root || (root->role.level < 1) || > > + (root->role.level > PT64_ROOT_MAX_LEVEL))) { > > + iter->valid = false; > > + return; > > + } > > > > I saw many usages of WARN_ON_ONCE() and WARN_ON() in KVM. And just wonder, > is there any criteria for KVM when to use which? Heh, already a step ahead of you :-) https://lore.kernel.org/all/20230721230006.2337941-5-seanjc@xxxxxxxxxx