From: Ackerley Tng via B4 Relay <devnull+ackerleytng.google.com@kernel.org>
To: Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Shuah Khan <skhan@linuxfoundation.org>,
Tianrui Zhao <zhaotianrui@loongson.cn>,
Bibo Mao <maobibo@loongson.cn>,
Huacai Chen <chenhuacai@kernel.org>,
WANG Xuerui <kernel@xen0n.name>,
Sean Christopherson <seanjc@google.com>,
Thomas Gleixner <tglx@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Fuad Tabba <tabba@google.com>,
vannapurve@google.com, x86@kernel.org,
"H. Peter Anvin" <hpa@zytor.com>
Cc: kvm@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, loongarch@lists.linux.dev,
Ackerley Tng <ackerleytng@google.com>
Subject: [PATCH RFC 02/12] Documentation: KVM: Consolidate notes about cpu_read_lock() and kvm_lock
Date: Wed, 27 May 2026 08:33:14 -0700 [thread overview]
Message-ID: <20260527-kvm-locking-docs-v1-2-4fe8b602ff47@google.com> (raw)
In-Reply-To: <20260527-kvm-locking-docs-v1-0-4fe8b602ff47@google.com>
From: Ackerley Tng <ackerleytng@google.com>
Move the detail about cpu_read_lock() and kvm_lock to where the acquisition
order is mentioned.
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
Documentation/virt/kvm/locking.rst | 12 +++++-------
1 file changed, 5 insertions(+), 7 deletions(-)
diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst
index 5564c8b38b9cc..1e8cbbe3ba706 100644
--- a/Documentation/virt/kvm/locking.rst
+++ b/Documentation/virt/kvm/locking.rst
@@ -10,6 +10,11 @@ KVM Lock Overview
The acquisition orders for mutexes are as follows:
- cpus_read_lock() is taken outside kvm_lock
+ - Taking cpus_read_lock() outside of kvm_lock is problematic,
+ despite it being the official ordering, as it is quite easy to
+ unknowingly trigger cpus_read_lock() while holding kvm_lock.
+ Use caution when walking vm_list, e.g. avoid complex operations
+ when possible.
- kvm_usage_lock is taken outside cpus_read_lock()
@@ -28,13 +33,6 @@ The acquisition orders for mutexes are as follows:
are taken on the waiting side when modifying memslots, so MMU notifiers
must not take either kvm->slots_lock or kvm->slots_arch_lock.
-cpus_read_lock() vs kvm_lock:
-
-- Taking cpus_read_lock() outside of kvm_lock is problematic, despite that
- being the official ordering, as it is quite easy to unknowingly trigger
- cpus_read_lock() while holding kvm_lock. Use caution when walking vm_list,
- e.g. avoid complex operations when possible.
-
For SRCU:
- ``synchronize_srcu(&kvm->srcu)`` is called inside critical sections
--
2.54.0.823.g6e5bcc1fc9-goog
next prev parent reply other threads:[~2026-05-27 15:33 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-27 15:33 [PATCH RFC 00/12] Document synchronization used in managing guest faults Ackerley Tng via B4 Relay
2026-05-27 15:33 ` [PATCH RFC 01/12] Documentation: KVM: Elaborate comment on kvm_usage_lock Ackerley Tng via B4 Relay
2026-06-25 18:12 ` Sean Christopherson
2026-05-27 15:33 ` Ackerley Tng via B4 Relay [this message]
2026-06-25 18:12 ` [PATCH RFC 02/12] Documentation: KVM: Consolidate notes about cpu_read_lock() and kvm_lock Sean Christopherson
2026-05-27 15:33 ` [PATCH RFC 03/12] Documentation: KVM: Consolidate notes about kvm->slots_lock and irq_lock Ackerley Tng via B4 Relay
2026-06-25 18:12 ` Sean Christopherson
2026-05-27 15:33 ` [PATCH RFC 04/12] Documentation: KVM: Turn - into bullet point Ackerley Tng via B4 Relay
2026-05-27 15:33 ` [PATCH RFC 05/12] Documentation: KVM: Explain what rule the exception section is meant for Ackerley Tng via B4 Relay
2026-05-27 15:33 ` [PATCH RFC 06/12] Documentation: KVM: Have actual headings for exceptions Ackerley Tng via B4 Relay
2026-05-27 15:33 ` [PATCH RFC 07/12] Documentation: KVM: Drop mention of kvm->lock in SRCU documentation Ackerley Tng via B4 Relay
2026-05-27 15:33 ` [PATCH RFC 08/12] Documentation: KVM: Add example for kvm->srcu in relation to mutex/lock Ackerley Tng via B4 Relay
2026-06-25 18:17 ` Sean Christopherson
2026-05-27 15:33 ` [PATCH RFC 09/12] Documentation: KVM: Document synchronization for managing guest faults Ackerley Tng via B4 Relay
2026-05-27 15:33 ` [PATCH RFC 10/12] KVM: guest_memfd: Clarify comment about gmem.file vs kvm->srcu Ackerley Tng via B4 Relay
2026-06-25 18:19 ` Sean Christopherson
2026-05-27 15:33 ` [PATCH RFC 11/12] KVM: mmu: Point users of host_pfn_mapping_level() to docs Ackerley Tng via B4 Relay
2026-05-27 15:33 ` [PATCH RFC 12/12] Documentation: KVM: Focus acquisition order section on preventing deadlocks Ackerley Tng via B4 Relay
2026-06-25 18:25 ` Sean Christopherson
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