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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id w1sm1318093wmc.18.2020.09.01.03.36.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Sep 2020 03:36:41 -0700 (PDT) From: Vitaly Kuznetsov To: Sean Christopherson , Jim Mattson Cc: Paolo Bonzini , Wanpeng Li , kvm list , LKML Subject: Re: [PATCH] KVM: VMX: fix crash cleanup when KVM wasn't used In-Reply-To: <20200825000920.GB15046@sjchrist-ice> References: <20200401081348.1345307-1-vkuznets@redhat.com> <20200822034046.GE4769@sjchrist-ice> <20200825000920.GB15046@sjchrist-ice> Date: Tue, 01 Sep 2020 12:36:40 +0200 Message-ID: <87pn75wzpj.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sean Christopherson writes: > On Mon, Aug 24, 2020 at 03:45:26PM -0700, Jim Mattson wrote: >> On Mon, Aug 24, 2020 at 11:57 AM Jim Mattson wrote: >> > >> > On Fri, Aug 21, 2020 at 8:40 PM Sean Christopherson >> > wrote: >> > > I agree the code is a mess (kvm_init() and kvm_exit() included), but I'm >> > > pretty sure hardware_disable_nolock() is guaranteed to be a nop as it's >> > > impossible for kvm_usage_count to be non-zero if vmx_init() hasn't >> > > finished. >> > >> > Unless I'm missing something, there's no check for a non-zero >> > kvm_usage_count on this path. There is such a check in >> > hardware_disable_all_nolock(), but not in hardware_disable_nolock(). >> >> However, cpus_hardware_enabled shouldn't have any bits set, so >> everything's fine. Nothing to see here, after all. > > Ugh, I forgot that hardware_disable_all_nolock() does a BUG_ON() instead of > bailing on !kvm_usage_count. But we can't hit this BUG_ON(), right? I'm failing to see how hardware_disable_all_nolock() can be reached with kvm_usage_count==0. -- Vitaly