From: Ben Gardon <bgardon@google.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>, Peter Xu <peterx@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Peter Shier <pshier@google.com>,
Peter Feiner <pfeiner@google.com>,
Junaid Shahid <junaids@google.com>,
Jim Mattson <jmattson@google.com>,
Yulei Zhang <yulei.kernel@gmail.com>,
Wanpeng Li <kernellwp@gmail.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Xiao Guangrong <xiaoguangrong.eric@gmail.com>,
Ben Gardon <bgardon@google.com>
Subject: [PATCH v2 13/13] KVM: x86/mmu: Tear down roots in fast invalidation thread
Date: Thu, 1 Apr 2021 16:37:36 -0700 [thread overview]
Message-ID: <20210401233736.638171-14-bgardon@google.com> (raw)
In-Reply-To: <20210401233736.638171-1-bgardon@google.com>
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 <bgardon@google.com>
---
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
next prev parent reply other threads:[~2021-04-01 23:38 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-01 23:37 [PATCH v2 00/13] More parallel operations for the TDP MMU Ben Gardon
2021-04-01 23:37 ` [PATCH v2 01/13] KVM: x86/mmu: Re-add const qualifier in kvm_tdp_mmu_zap_collapsible_sptes Ben Gardon
2021-05-26 21:25 ` Sean Christopherson
2021-04-01 23:37 ` [PATCH v2 02/13] KVM: x86/mmu: Move kvm_mmu_(get|put)_root to TDP MMU Ben Gardon
2021-04-01 23:37 ` [PATCH v2 03/13] KVM: x86/mmu: use tdp_mmu_free_sp to free roots Ben Gardon
2021-04-01 23:37 ` [PATCH v2 04/13] KVM: x86/mmu: Merge TDP MMU put and free root Ben Gardon
2021-04-01 23:37 ` [PATCH v2 05/13] KVM: x86/mmu: Refactor yield safe root iterator Ben Gardon
2021-04-01 23:37 ` [PATCH v2 06/13] KVM: x86/mmu: Make TDP MMU root refcount atomic Ben Gardon
2021-04-01 23:37 ` [PATCH v2 07/13] KVM: x86/mmu: handle cmpxchg failure in kvm_tdp_mmu_get_root Ben Gardon
2021-04-01 23:37 ` [PATCH v2 08/13] KVM: x86/mmu: Protect the tdp_mmu_roots list with RCU Ben Gardon
2021-04-01 23:37 ` [PATCH v2 09/13] KVM: x86/mmu: Allow zap gfn range to operate under the mmu read lock Ben Gardon
2021-04-02 7:53 ` Paolo Bonzini
2021-04-12 18:21 ` Ben Gardon
2021-04-01 23:37 ` [PATCH v2 10/13] KVM: x86/mmu: Allow zapping collapsible SPTEs to use MMU " Ben Gardon
2021-04-02 11:14 ` Paolo Bonzini
2021-04-01 23:37 ` [PATCH v2 11/13] KVM: x86/mmu: Allow enabling / disabling dirty logging under " Ben Gardon
2021-04-01 23:37 ` [PATCH v2 12/13] KVM: x86/mmu: Fast invalidation for TDP MMU Ben Gardon
2021-04-01 23:37 ` Ben Gardon [this message]
2021-04-02 11:43 ` [PATCH v2 00/13] More parallel operations for the " Paolo Bonzini
2021-05-26 21:34 ` Sean Christopherson
2021-05-27 11:41 ` Paolo Bonzini
2021-05-27 15:26 ` Sean Christopherson
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