On Tue, Nov 5, 2024 at 10:43 AM James Houghton <jthoughton@xxxxxxxxxx> wrote:
>
> static inline u64 kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 old_spte,
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 4508d868f1cd..f5b4f1060fff 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -178,6 +178,15 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
> ((_only_valid) && (_root)->role.invalid))) { \
> } else
>
> +/*
> + * Iterate over all TDP MMU roots in an RCU read-side critical section.
> + */
> +#define for_each_valid_tdp_mmu_root_rcu(_kvm, _root, _as_id) \
> + list_for_each_entry_rcu(_root, &_kvm->arch.tdp_mmu_roots, link) \
> + if ((_as_id >= 0 && kvm_mmu_page_as_id(_root) != _as_id) || \
> + (_root)->role.invalid) { \
> + } else
> +
Venkatesh noticed that this function is unused in this patch. This was
a mistake in the latest rebase. The diff should have been applied:
@@ -1192,15 +1206,15 @@ static bool __kvm_tdp_mmu_age_gfn_range(struct kvm *kvm,
struct tdp_iter iter;
bool ret = false;
+ guard(rcu)();
+
/*
* Don't support rescheduling, none of the MMU notifiers that funnel
* into this helper allow blocking; it'd be dead, wasteful code. Note,
* this helper must NOT be used to unmap GFNs, as it processes only
* valid roots!
*/
- for_each_valid_tdp_mmu_root(kvm, root, range->slot->as_id) {
- guard(rcu)();
-
+ for_each_valid_tdp_mmu_root_rcu(kvm, root, range->slot->as_id) {
tdp_root_for_each_leaf_pte(iter, root, range->start,
range->end) {
if (!is_accessed_spte(iter.old_spte))
continue;
This bug will show up as a LOCKDEP warning on CONFIG_PROVE_RCU_LIST=y
kernels, as list_for_each_entry_rcu() is called outside of an RCU
read-side critical section.
