The root page table in the TDP MMU paging structure is not protected with RCU, but rather by the root_count in the associated SP. As a result it is safe for tdp_iter_root_pt to simply return a u64 *. This sidesteps the complexities assoicated with propagating the __rcu annotation around.
Reported-by: kernel test robot <lkp@xxxxxxxxx> Signed-off-by: Ben Gardon <[email protected]> --- arch/x86/kvm/mmu/tdp_iter.c | 10 ++++++++-- arch/x86/kvm/mmu/tdp_iter.h | 2 +- arch/x86/kvm/mmu/tdp_mmu.c | 4 ++-- 3 files changed, 11 insertions(+), 5 deletions(-) diff --git a/arch/x86/kvm/mmu/tdp_iter.c b/arch/x86/kvm/mmu/tdp_iter.c index e5f148106e20..8e2c053533b6 100644 --- a/arch/x86/kvm/mmu/tdp_iter.c +++ b/arch/x86/kvm/mmu/tdp_iter.c @@ -159,8 +159,14 @@ void tdp_iter_next(struct tdp_iter *iter) iter->valid = false; } -tdp_ptep_t tdp_iter_root_pt(struct tdp_iter *iter) +u64 *tdp_iter_root_pt(struct tdp_iter *iter) { - return iter->pt_path[iter->root_level - 1]; + /* + * Though it is stored in an array of tdp_ptep_t for convenience, + * the root PT is not actually protected by RCU, but by the root + * count on the associated struct kvm_mmu_page. As a result it's + * safe to rcu_dereference and return the value here. + */ + return rcu_dereference(iter->pt_path[iter->root_level - 1]); } diff --git a/arch/x86/kvm/mmu/tdp_iter.h b/arch/x86/kvm/mmu/tdp_iter.h index 4cc177d75c4a..5a47c57810ab 100644 --- a/arch/x86/kvm/mmu/tdp_iter.h +++ b/arch/x86/kvm/mmu/tdp_iter.h @@ -62,6 +62,6 @@ tdp_ptep_t spte_to_child_pt(u64 pte, int level); void tdp_iter_start(struct tdp_iter *iter, u64 *root_pt, int root_level, int min_level, gfn_t next_last_level_gfn); void tdp_iter_next(struct tdp_iter *iter); -tdp_ptep_t tdp_iter_root_pt(struct tdp_iter *iter); +u64 *tdp_iter_root_pt(struct tdp_iter *iter); #endif /* __KVM_X86_MMU_TDP_ITER_H */ diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 5387ac040f66..6c8824bcc2f2 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -558,7 +558,7 @@ static inline void __tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter, u64 new_spte, bool record_acc_track, bool record_dirty_log) { - tdp_ptep_t root_pt = tdp_iter_root_pt(iter); + u64 *root_pt = tdp_iter_root_pt(iter); struct kvm_mmu_page *root = sptep_to_sp(root_pt); int as_id = kvm_mmu_page_as_id(root); @@ -653,7 +653,7 @@ static inline bool tdp_mmu_iter_cond_resched(struct kvm *kvm, WARN_ON(iter->gfn > iter->next_last_level_gfn); - tdp_iter_start(iter, iter->pt_path[iter->root_level - 1], + tdp_iter_start(iter, tdp_iter_root_pt(iter), iter->root_level, iter->min_level, iter->next_last_level_gfn); -- 2.31.0.rc2.261.g7f71774620-goog
