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Mon, 01 Dec 2025 19:48:14 -0800 (PST) Received: from zeus ([2405:6580:83a0:7600:6e93:a15a:9134:ae1f]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29bceb559d6sm138403325ad.94.2025.12.01.19.48.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Dec 2025 19:48:14 -0800 (PST) Date: Tue, 2 Dec 2025 12:48:10 +0900 From: Ryosuke Yasuoka To: pbonzini@redhat.com, vkuznets@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com Cc: x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86/kvm: Avoid freeing stack-allocated node in kvm_async_pf_queue_task Message-ID: References: <20251122090828.1416464-1-ryasuoka@redhat.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251122090828.1416464-1-ryasuoka@redhat.com> On Sat, Nov 22, 2025 at 06:08:24PM +0900, Ryosuke Yasuoka wrote: > kvm_async_pf_queue_task() can incorrectly remove a node allocated on the > stack of kvm_async_pf_task_wait_schedule(). This occurs when a task > request a PF while another task's PF request with the same token is > still pending. Currently, kvm_async_pf_queue_task() assumes that any > entry in the list is a dummy entry and tries to kfree(). To fix this, > add a dummy flag to the node structure and the function should check > this flag and kfree() only if it is a dummy entry. > > Signed-off-by: Ryosuke Yasuoka > --- > arch/x86/kernel/kvm.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index b67d7c59dca0..2c92ec528379 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -88,6 +88,7 @@ struct kvm_task_sleep_node { > struct swait_queue_head wq; > u32 token; > int cpu; > + bool dummy; > }; > > static struct kvm_task_sleep_head { > @@ -119,10 +120,17 @@ static bool kvm_async_pf_queue_task(u32 token, struct kvm_task_sleep_node *n) > raw_spin_lock(&b->lock); > e = _find_apf_task(b, token); > if (e) { > + struct kvm_task_sleep_node *dummy = NULL; > + > /* dummy entry exist -> wake up was delivered ahead of PF */ > - hlist_del(&e->link); > + /* Otherwise it should not be freed here. */ > + if (e->dummy) { > + hlist_del(&e->link); > + dummy = e; > + } > + > raw_spin_unlock(&b->lock); > - kfree(e); > + kfree(dummy); > return false; > } > > @@ -230,6 +238,7 @@ static void kvm_async_pf_task_wake(u32 token) > } > dummy->token = token; > dummy->cpu = smp_processor_id(); > + dummy->dummy = true; > init_swait_queue_head(&dummy->wq); > hlist_add_head(&dummy->link, &b->list); > dummy = NULL; > > base-commit: 2eba5e05d9bcf4cdea995ed51b0f07ba0275794a > -- > 2.51.0 Hi all, It's just a gentle ping on this patch. Please let me know if thare any changes required. Any feedbacks are welcome. Here is a original patch's link: https://lore.kernel.org/all/20251122090828.1416464-1-ryasuoka@redhat.com/ Thank you Ryosuke