From: Sean Christopherson <seanjc@google.com>
To: "zoudongjie (A)" <zoudongjie@huawei.com>
Cc: "pbonzini@redhat.com" <pbonzini@redhat.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"bp@alien8.de" <bp@alien8.de>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"x86@kernel.org" <x86@kernel.org>,
"hpa@zytor.com" <hpa@zytor.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Chenzhendong (alex)" <alex.chen@huawei.com>,
luolongmin <luolongmin@huawei.com>,
"Mujinsheng (DxJanesir)" <mujinsheng@huawei.com>,
"chenjianfei (D)" <chenjianfei3@huawei.com>,
"Fangyi (Eric)" <eric.fangyi@huawei.com>,
"lishan (E)" <lishan24@huawei.com>,
Renxuming <renxuming@huawei.com>,
suxiaodong <suxiaodong1@huawei.com>,
"caijunjie (A)" <caijunjie15@h-partners.com>
Subject: Re: [Question Consultation] KVM: x86: No lock protection was applied in handle_ept_misconfig of kernel 5.10?
Date: Wed, 9 Jul 2025 05:42:17 -0700 [thread overview]
Message-ID: <aG5jqVJ0S2nDFMch@google.com> (raw)
In-Reply-To: <fb4c14aa629a4dddb44d0fa9c4f7b498@huawei.com>
On Wed, Jul 09, 2025, zoudongjie (A) wrote:
> Hi all,
>
> I noticed that in handle_ept_misconfig(), kvm_io_bus_write() is called. And
> within kvm_io_bus_write(), BUS is obtained through srcu_dereference(). During
> this process, kvm->slots_lock is not acquired, nor is srcu_read_lock() called
> for protection.
srcu_read_lock() is called via kvm_vcpu_srcu_read_lock() in the VM-Exit path of
vcpu_enter_guest(). KVM grabs kvm->srcu early during KVM_RUN (again via
kvm_vcpu_srcu_read_lock(), in kvm_arch_vcpu_ioctl_run()), and holds the lock for
essentially the entire duration of KVM_RUN. SRCU protection is temporarily
dropped only when the vCPU blocks and when the vCPU enters the guest.
> If another process is synchronizing BUS at the same time,
> synchronize_srcu_expedited() cannot safely reclaim space(it cannot protect
> srcu_dereference() outside the critical section?), how can we ensure that BUS
> obtained by kvm_io_bus_write() is the latest?
>
> Thanks,
> Junjie Cai
>
> Reported by: Junjie Cai <caijunjie15@h-partners.com>
prev parent reply other threads:[~2025-07-09 12:42 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-09 6:32 zoudongjie (A)
2025-07-09 12:42 ` Sean Christopherson [this message]
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