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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



  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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