From 614f6970aa70242a3f8a8051b01244c029f77b2a Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Wed, 2 Mar 2022 08:51:05 -0500 Subject: [PATCH] KVM: x86/mmu: do not allow readers to acquire references to invalid roots Remove the "shared" argument of for_each_tdp_mmu_root_yield_safe, thus ensuring that readers do not ever acquire a reference to an invalid root. After this patch, all readers except kvm_tdp_mmu_zap_invalidated_roots() treat refcount=0/valid, refcount=0/invalid and refcount=1/invalid in exactly the same way. kvm_tdp_mmu_zap_invalidated_roots() is different but it also does not acquire a reference to the invalid root, and it cannot see refcount=0/invalid because it is guaranteed to run after kvm_tdp_mmu_invalidate_all_roots(). Opportunistically add a lockdep assertion to the yield-safe iterator. Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/tdp_mmu.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index d39593b9ac9e..79bc48ddb69d 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -166,14 +166,15 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm, for (_root = tdp_mmu_next_root(_kvm, NULL, _shared, _only_valid); \ _root; \ _root = tdp_mmu_next_root(_kvm, _root, _shared, _only_valid)) \ - if (kvm_mmu_page_as_id(_root) != _as_id) { \ + if (kvm_lockdep_assert_mmu_lock_held(_kvm, _shared) && \ + kvm_mmu_page_as_id(_root) != _as_id) { \ } else #define for_each_valid_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared) \ __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, true) -#define for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared) \ - __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, false) +#define for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id) \ + __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, false, false) /* * Iterate over all TDP MMU roots. Requires that mmu_lock be held for write, @@ -808,7 +809,7 @@ bool __kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, int as_id, gfn_t start, { struct kvm_mmu_page *root; - for_each_tdp_mmu_root_yield_safe(kvm, root, as_id, false) + for_each_tdp_mmu_root_yield_safe(kvm, root, as_id) flush = zap_gfn_range(kvm, root, start, end, can_yield, flush, false); -- 2.20.1