From: Hillf Danton <hdanton@sina.com>
To: David Woodhouse <dwmw2@infradead.org>
Cc: linux-kernel@vger.kernel.org, rcu@vger.kernel.org,
kvm@vger.kernel.org, linux-rt-devel@lists.linux.dev,
linux-kselftest@vger.kernel.org,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <seanjc@google.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [PATCH 01/17] KVM: pfncache: Use atomic SRCU for readers instead of a rwlock
Date: Mon, 21 Sep 2026 09:42:56 +0800 [thread overview]
Message-ID: <20260921014301.248-1-hdanton@sina.com> (raw)
In-Reply-To: <20260920211920.928306-2-dwmw2@infradead.org>
On Sun, 20 Sep 2026 21:49:29 +0100 David Woodhouse wrote:
>
> Replace the per-cache rwlock with a dedicated per-VM atomic SRCU
> domain (kvm->gpc_srcu) for the read side. Readers now run under
> srcu_read_lock_atomic() alone — preemption disabled and non-blocking
> enforced, which every GPC read-side section already satisfied as a
> former rwlock critical section. It works in any context
> (including hardirq and sched-out paths) and never fails or spins,
> eliminating the
> read_trylock() contortions in the atomic paths, the double-lock dance
> with the lockdep subclass hack in the runstate update, and the
> PREEMPT_RT problems inherent to taking an rwlock in those contexts.
> In particular, kvm_xen_set_evtchn_fast() is called from hardirq
> context (timer callback, kvm_arch_set_irq_inatomic()), where taking
> gpc->lock is a sleeping-lock-in-atomic-context bug on PREEMPT_RT.
>
Given the preempt_disable() in srcu_read_lock_atomic(), as PREEMPT_RT
has no way of handling preempt_disable(), you need to add another
version of srcu_read_lock_atomic() with preempt_disable() replaced with
something like rcu_read_lock().
next prev parent reply other threads:[~2026-09-21 1:43 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-20 20:49 [PATCH 00/17] KVM: Use atomic SRCU for gfn-to-pfn cache, reinstate guest mode for x86 nesting David Woodhouse
2026-09-20 20:49 ` [PATCH 01/17] KVM: pfncache: Use atomic SRCU for readers instead of a rwlock David Woodhouse
2026-09-20 21:55 ` sashiko-bot
2026-09-21 1:42 ` Hillf Danton [this message]
2026-09-21 9:54 ` David Woodhouse
2026-09-21 11:21 ` Hillf Danton
2026-09-21 11:29 ` Paolo Bonzini
2026-09-20 20:49 ` [PATCH 02/17] KVM: x86/xen: Extract delivery of event to vCPU into a separate helper David Woodhouse
2026-09-20 20:49 ` [PATCH 03/17] KVM: x86/xen: Explicitly tag "shared info" page as never being dirty tracked David Woodhouse
2026-09-20 20:49 ` [PATCH 04/17] KVM: x86/xen: Don't dirty track "vCPU info" page David Woodhouse
2026-09-20 20:49 ` [PATCH 05/17] KVM: x86: Request the guest TLB flush from record_steal_time() David Woodhouse
2026-09-20 20:49 ` [PATCH 06/17] KVM: x86: Use gfn_to_pfn_cache for steal time / preempted status David Woodhouse
2026-09-20 22:06 ` sashiko-bot
2026-09-20 20:49 ` [PATCH 07/17] KVM: pfncache: Add guest-mode pinning (GUEST_USES_PFN successor) David Woodhouse
2026-09-20 21:53 ` sashiko-bot
2026-09-21 14:17 ` David Woodhouse
2026-09-20 20:49 ` [PATCH 08/17] KVM: pfncache: Return -EAGAIN for a lookup which hits an invalid memslot David Woodhouse
2026-09-20 21:53 ` sashiko-bot
2026-09-20 20:49 ` [PATCH 09/17] KVM: x86: Post KVM_REQ_GET_NESTED_STATE_PAGES on memslot updates David Woodhouse
2026-09-20 20:49 ` [PATCH 10/17] KVM: nVMX: Implement cache for L1 MSR bitmap David Woodhouse
2026-09-20 21:56 ` sashiko-bot
2026-09-20 20:49 ` [PATCH 11/17] KVM: nVMX: Use pinned pfncache for L1 APIC virtualization pages David Woodhouse
2026-09-20 21:57 ` sashiko-bot
2026-09-21 14:31 ` David Woodhouse
2026-09-20 20:49 ` [PATCH 12/17] KVM: selftests: Add nested VMX APIC cache invalidation test David Woodhouse
2026-09-20 21:51 ` sashiko-bot
2026-09-20 20:49 ` [PATCH 13/17] KVM: x86: Move nested GPC lock helpers to x86.h as kvm_gpc_lock_page() David Woodhouse
2026-09-20 20:49 ` [PATCH 14/17] KVM: nSVM: Use a gfn_to_pfn_cache for the vmcb12 page David Woodhouse
2026-09-20 20:49 ` [PATCH 15/17] KVM: nSVM: Cache L1's MSR permissions map pages David Woodhouse
2026-09-20 20:49 ` [PATCH 16/17] KVM: nSVM: Cache L1's IO " David Woodhouse
2026-09-20 20:49 ` [PATCH 17/17] KVM: selftests: Add nested transition benchmark David Woodhouse
2026-09-20 21:52 ` sashiko-bot
2026-09-21 14:10 ` [PATCH 00/17] KVM: Use atomic SRCU for gfn-to-pfn cache, reinstate guest mode for x86 nesting David Woodhouse
2026-09-22 3:16 ` KunWu Chan
2026-09-22 10:37 ` David Woodhouse
2026-09-23 9:54 ` Kunwu Chan
2026-09-23 12:05 ` David Woodhouse
2026-09-23 15:58 ` KunWu Chan
2026-09-23 16:07 ` David Woodhouse
2026-09-23 16:26 ` KunWu Chan
2026-09-23 16:46 ` David Woodhouse
2026-09-24 1:04 ` KunWu Chan
2026-09-23 21:56 ` David Woodhouse
2026-09-24 0:59 ` KunWu Chan
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