From: Paolo Bonzini <pbonzini@redhat.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
David Hildenbrand <david@redhat.com>,
David Matlack <dmatlack@google.com>,
Ben Gardon <bgardon@google.com>,
Mingwei Zhang <mizhang@google.com>
Subject: [PATCH v4 11/30] KVM: x86/mmu: Add helpers to read/write TDP MMU SPTEs and document RCU
Date: Thu, 3 Mar 2022 14:38:23 -0500 [thread overview]
Message-ID: <20220303193842.370645-12-pbonzini@redhat.com> (raw)
In-Reply-To: <20220303193842.370645-1-pbonzini@redhat.com>
From: Sean Christopherson <seanjc@google.com>
Add helpers to read and write TDP MMU SPTEs instead of open coding
rcu_dereference() all over the place, and to provide a convenient
location to document why KVM doesn't exempt holding mmu_lock for write
from having to hold RCU (and any future changes to the rules).
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Message-Id: <20220226001546.360188-11-seanjc@google.com>
Reviewed-by: Mingwei Zhang <mizhang@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/mmu/tdp_iter.c | 6 +++---
arch/x86/kvm/mmu/tdp_iter.h | 16 ++++++++++++++++
arch/x86/kvm/mmu/tdp_mmu.c | 6 +++---
3 files changed, 22 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/mmu/tdp_iter.c b/arch/x86/kvm/mmu/tdp_iter.c
index be3f096db2eb..6d3b3e5a5533 100644
--- a/arch/x86/kvm/mmu/tdp_iter.c
+++ b/arch/x86/kvm/mmu/tdp_iter.c
@@ -12,7 +12,7 @@ static void tdp_iter_refresh_sptep(struct tdp_iter *iter)
{
iter->sptep = iter->pt_path[iter->level - 1] +
SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level);
- iter->old_spte = READ_ONCE(*rcu_dereference(iter->sptep));
+ iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep);
}
static gfn_t round_gfn_for_level(gfn_t gfn, int level)
@@ -89,7 +89,7 @@ static bool try_step_down(struct tdp_iter *iter)
* Reread the SPTE before stepping down to avoid traversing into page
* tables that are no longer linked from this entry.
*/
- iter->old_spte = READ_ONCE(*rcu_dereference(iter->sptep));
+ iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep);
child_pt = spte_to_child_pt(iter->old_spte, iter->level);
if (!child_pt)
@@ -123,7 +123,7 @@ static bool try_step_side(struct tdp_iter *iter)
iter->gfn += KVM_PAGES_PER_HPAGE(iter->level);
iter->next_last_level_gfn = iter->gfn;
iter->sptep++;
- iter->old_spte = READ_ONCE(*rcu_dereference(iter->sptep));
+ iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep);
return true;
}
diff --git a/arch/x86/kvm/mmu/tdp_iter.h b/arch/x86/kvm/mmu/tdp_iter.h
index 216ebbe76ddd..bb9b581f1ee4 100644
--- a/arch/x86/kvm/mmu/tdp_iter.h
+++ b/arch/x86/kvm/mmu/tdp_iter.h
@@ -9,6 +9,22 @@
typedef u64 __rcu *tdp_ptep_t;
+/*
+ * TDP MMU SPTEs are RCU protected to allow paging structures (non-leaf SPTEs)
+ * to be zapped while holding mmu_lock for read. Holding RCU isn't required for
+ * correctness if mmu_lock is held for write, but plumbing "struct kvm" down to
+ * the lower depths of the TDP MMU just to make lockdep happy is a nightmare, so
+ * all accesses to SPTEs are done under RCU protection.
+ */
+static inline u64 kvm_tdp_mmu_read_spte(tdp_ptep_t sptep)
+{
+ return READ_ONCE(*rcu_dereference(sptep));
+}
+static inline void kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 val)
+{
+ WRITE_ONCE(*rcu_dereference(sptep), val);
+}
+
/*
* A TDP iterator performs a pre-order walk over a TDP paging structure.
*/
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 22b0c03b673b..371b6a108736 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -595,7 +595,7 @@ static inline int tdp_mmu_zap_spte_atomic(struct kvm *kvm,
* here since the SPTE is going from non-present
* to non-present.
*/
- WRITE_ONCE(*rcu_dereference(iter->sptep), 0);
+ kvm_tdp_mmu_write_spte(iter->sptep, 0);
return 0;
}
@@ -634,7 +634,7 @@ static inline void __tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter,
*/
WARN_ON(is_removed_spte(iter->old_spte));
- WRITE_ONCE(*rcu_dereference(iter->sptep), new_spte);
+ kvm_tdp_mmu_write_spte(iter->sptep, new_spte);
__handle_changed_spte(kvm, iter->as_id, iter->gfn, iter->old_spte,
new_spte, iter->level, false);
@@ -1069,7 +1069,7 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
* because the new value informs the !present
* path below.
*/
- iter.old_spte = READ_ONCE(*rcu_dereference(iter.sptep));
+ iter.old_spte = kvm_tdp_mmu_read_spte(iter.sptep);
}
if (!is_shadow_present_pte(iter.old_spte)) {
--
2.31.1
next prev parent reply other threads:[~2022-03-03 19:39 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-03 19:38 [PATCH v4 00/30] KVM: x86/mmu: Overhaul TDP MMU zapping and flushing Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 01/30] KVM: x86/mmu: Check for present SPTE when clearing dirty bit in TDP MMU Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 02/30] KVM: x86/mmu: Fix wrong/misleading comments in TDP MMU fast zap Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 03/30] KVM: x86/mmu: Formalize TDP MMU's (unintended?) deferred TLB flush logic Paolo Bonzini
2022-03-03 23:39 ` Mingwei Zhang
2022-03-03 19:38 ` [PATCH v4 04/30] KVM: x86/mmu: Document that zapping invalidated roots doesn't need to flush Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 05/30] KVM: x86/mmu: Require mmu_lock be held for write in unyielding root iter Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 06/30] KVM: x86/mmu: only perform eager page splitting on valid roots Paolo Bonzini
2022-03-03 20:03 ` Sean Christopherson
2022-03-03 19:38 ` [PATCH v4 07/30] KVM: x86/mmu: do not allow readers to acquire references to invalid roots Paolo Bonzini
2022-03-03 20:12 ` Sean Christopherson
2022-03-03 19:38 ` [PATCH v4 08/30] KVM: x86/mmu: Check for !leaf=>leaf, not PFN change, in TDP MMU SP removal Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 09/30] KVM: x86/mmu: Batch TLB flushes from TDP MMU for MMU notifier change_spte Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 10/30] KVM: x86/mmu: Drop RCU after processing each root in MMU notifier hooks Paolo Bonzini
2022-03-03 19:38 ` Paolo Bonzini [this message]
2022-03-03 19:38 ` [PATCH v4 12/30] KVM: x86/mmu: WARN if old _or_ new SPTE is REMOVED in non-atomic path Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 13/30] KVM: x86/mmu: Refactor low-level TDP MMU set SPTE helper to take raw values Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 14/30] KVM: x86/mmu: Zap only the target TDP MMU shadow page in NX recovery Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 15/30] KVM: x86/mmu: Skip remote TLB flush when zapping all of TDP MMU Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 16/30] KVM: x86/mmu: Add dedicated helper to zap TDP MMU root shadow page Paolo Bonzini
2022-03-04 0:07 ` Mingwei Zhang
2022-03-03 19:38 ` [PATCH v4 17/30] KVM: x86/mmu: Require mmu_lock be held for write to zap TDP MMU range Paolo Bonzini
2022-03-04 0:14 ` Mingwei Zhang
2022-03-03 19:38 ` [PATCH v4 18/30] KVM: x86/mmu: Zap only TDP MMU leafs in kvm_zap_gfn_range() Paolo Bonzini
2022-03-04 1:16 ` Mingwei Zhang
2022-03-04 16:11 ` Sean Christopherson
2022-03-04 18:00 ` Mingwei Zhang
2022-03-04 18:42 ` Sean Christopherson
2022-03-11 15:09 ` Vitaly Kuznetsov
2022-03-13 18:40 ` Mingwei Zhang
2022-03-25 15:13 ` Sean Christopherson
2022-03-26 18:10 ` Mingwei Zhang
2022-03-28 15:06 ` Sean Christopherson
2022-03-03 19:38 ` [PATCH v4 19/30] KVM: x86/mmu: Do remote TLB flush before dropping RCU in TDP MMU resched Paolo Bonzini
2022-03-04 1:19 ` Mingwei Zhang
2022-03-03 19:38 ` [PATCH v4 20/30] KVM: x86/mmu: Defer TLB flush to caller when freeing TDP MMU shadow pages Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 21/30] KVM: x86/mmu: Zap invalidated roots via asynchronous worker Paolo Bonzini
2022-03-03 20:54 ` Sean Christopherson
2022-03-03 21:06 ` Sean Christopherson
2022-03-03 21:20 ` Sean Christopherson
2022-03-03 21:32 ` Sean Christopherson
2022-03-04 6:48 ` Paolo Bonzini
2022-03-04 16:02 ` Sean Christopherson
2022-03-04 18:11 ` Paolo Bonzini
2022-03-05 0:34 ` Sean Christopherson
2022-03-05 19:53 ` Paolo Bonzini
2022-03-08 21:29 ` Sean Christopherson
2022-03-11 17:50 ` Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 22/30] KVM: x86/mmu: Allow yielding when zapping GFNs for defunct TDP MMU root Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 23/30] KVM: x86/mmu: Zap roots in two passes to avoid inducing RCU stalls Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 24/30] KVM: x86/mmu: Zap defunct roots via asynchronous worker Paolo Bonzini
2022-03-03 22:08 ` Sean Christopherson
2022-03-03 19:38 ` [PATCH v4 25/30] KVM: x86/mmu: Check for a REMOVED leaf SPTE before making the SPTE Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 26/30] KVM: x86/mmu: WARN on any attempt to atomically update REMOVED SPTE Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 27/30] KVM: selftests: Move raw KVM_SET_USER_MEMORY_REGION helper to utils Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 28/30] KVM: selftests: Split out helper to allocate guest mem via memfd Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 29/30] KVM: selftests: Define cpu_relax() helpers for s390 and x86 Paolo Bonzini
2022-03-03 19:38 ` [PATCH v4 30/30] KVM: selftests: Add test to populate a VM with the max possible guest mem Paolo Bonzini
2022-03-08 14:47 ` Paolo Bonzini
2022-03-08 15:36 ` Christian Borntraeger
2022-03-08 21:09 ` Sean Christopherson
2022-03-08 17:25 ` [PATCH v4 00/30] KVM: x86/mmu: Overhaul TDP MMU zapping and flushing Paolo Bonzini
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