To avoid saddling a vCPU thread with the work of tearing down an entire paging structure, take a reference on each root before they become obsolete, so that the thread initiating the fast invalidation can tear down the paging structure and (most likely) release the last reference. As a bonus, this teardown can happen under the MMU lock in read mode so as not to block the progress of vCPU threads.
Signed-off-by: Ben Gardon <[email protected]> --- Changelog v2: -- rename kvm_tdp_mmu_zap_all_fast to kvm_tdp_mmu_zap_invalidated_roots arch/x86/kvm/mmu/mmu.c | 21 +++++++++++- arch/x86/kvm/mmu/tdp_mmu.c | 68 ++++++++++++++++++++++++++++++++++++++ arch/x86/kvm/mmu/tdp_mmu.h | 1 + 3 files changed, 89 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index ba0c65076200..5f2064ee7220 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -5441,6 +5441,18 @@ static void kvm_mmu_zap_all_fast(struct kvm *kvm) * will drop their references and allow the root count to * go to 0. * + * Also take a reference on all roots so that this thread + * can do the bulk of the work required to free the roots + * once they are invalidated. Without this reference, a + * vCPU thread might drop the last reference to a root and + * get stuck with tearing down the entire paging structure. + * + * Roots which have a zero refcount should be skipped as + * they're already being torn down. + * Already invalid roots should be referenced again so that + * they aren't freed before kvm_tdp_mmu_zap_all_fast is + * done with them. + * * This has essentially the same effect for the TDP MMU * as updating mmu_valid_gen above does for the shadow * MMU. @@ -5452,7 +5464,8 @@ static void kvm_mmu_zap_all_fast(struct kvm *kvm) * could drop the MMU lock and yield. */ list_for_each_entry(root, &kvm->arch.tdp_mmu_roots, link) - root->role.invalid = true; + if (refcount_inc_not_zero(&root->tdp_mmu_root_count)) + root->role.invalid = true; } /* @@ -5468,6 +5481,12 @@ static void kvm_mmu_zap_all_fast(struct kvm *kvm) kvm_zap_obsolete_pages(kvm); write_unlock(&kvm->mmu_lock); + + if (is_tdp_mmu_enabled(kvm)) { + read_lock(&kvm->mmu_lock); + kvm_tdp_mmu_zap_invalidated_roots(kvm); + read_unlock(&kvm->mmu_lock); + } } static bool kvm_has_zapped_obsolete_pages(struct kvm *kvm) diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 501722a524a7..0adcfa5750f6 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -798,6 +798,74 @@ void kvm_tdp_mmu_zap_all(struct kvm *kvm) kvm_flush_remote_tlbs(kvm); } +static struct kvm_mmu_page *next_invalidated_root(struct kvm *kvm, + struct kvm_mmu_page *prev_root) +{ + struct kvm_mmu_page *next_root; + + if (prev_root) + next_root = list_next_or_null_rcu(&kvm->arch.tdp_mmu_roots, + &prev_root->link, + typeof(*prev_root), link); + else + next_root = list_first_or_null_rcu(&kvm->arch.tdp_mmu_roots, + typeof(*next_root), link); + + while (next_root && !(next_root->role.invalid && + refcount_read(&next_root->tdp_mmu_root_count))) + next_root = list_next_or_null_rcu(&kvm->arch.tdp_mmu_roots, + &next_root->link, + typeof(*next_root), link); + + return next_root; +} + +/* + * Since kvm_mmu_zap_all_fast has acquired a reference to each + * invalidated root, they will not be freed until this function drops the + * reference. Before dropping that reference, tear down the paging + * structure so that whichever thread does drop the last reference + * only has to do a trivial ammount of work. Since the roots are invalid, + * no new SPTEs should be created under them. + */ +void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm) +{ + gfn_t max_gfn = 1ULL << (shadow_phys_bits - PAGE_SHIFT); + struct kvm_mmu_page *next_root; + struct kvm_mmu_page *root; + bool flush = false; + + lockdep_assert_held_read(&kvm->mmu_lock); + + rcu_read_lock(); + + root = next_invalidated_root(kvm, NULL); + + while (root) { + next_root = next_invalidated_root(kvm, root); + + rcu_read_unlock(); + + flush = zap_gfn_range(kvm, root, 0, max_gfn, true, flush, + true); + + /* + * Put the reference acquired in + * kvm_tdp_mmu_invalidate_roots + */ + kvm_tdp_mmu_put_root(kvm, root, true); + + root = next_root; + + rcu_read_lock(); + } + + rcu_read_unlock(); + + if (flush) + kvm_flush_remote_tlbs(kvm); +} + /* * Installs a last-level SPTE to handle a TDP page fault. * (NPT/EPT violation/misconfiguration) diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h index 8fa3e7421a93..f8db381e3059 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.h +++ b/arch/x86/kvm/mmu/tdp_mmu.h @@ -47,6 +47,7 @@ static inline bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp) sp->gfn, end, false, false, false); } void kvm_tdp_mmu_zap_all(struct kvm *kvm); +void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm); int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code, int map_writable, int max_level, kvm_pfn_t pfn, -- 2.31.0.208.g409f899ff0-goog
