Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Sean Christopherson <sean.j.christopherson@intel.com>,
        Jim Mattson <jmattson@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        kvm list <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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> <CALMp9eROXAOg_g=R8JRVfywY7uQXzBtVxKJYXq0dUcob-BfR-g@mail.gmail.com> <20200822034046.GE4769@sjchrist-ice> <CALMp9eRHh9KXO12k4GaoenSJazFnSaN68FTVxOGhE9Mxw-hf2A@mail.gmail.com> <CALMp9eS1HusEZvzLShuuuxQnReKgTtunsKLoy+2GMVJAaTrZ7A@mail.gmail.com> <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

Sean Christopherson <sean.j.christopherson@intel.com> 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 <jmattson@google.com> wrote:
>> >
>> > On Fri, Aug 21, 2020 at 8:40 PM Sean Christopherson
>> > <sean.j.christopherson@intel.com> 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