Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <fba8e829-0d28-8f4d-a8ce-84d533009eb9@redhat.com>
Date:   Mon, 24 Oct 2022 14:57:33 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.2.0
Subject: Re: [PATCH 3/4] KVM: introduce memory transaction semaphore
Content-Language: en-US
To:     Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Maxim Levitsky <mlevitsk@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        David Hildenbrand <david@redhat.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20221022154819.1823133-1-eesposit@redhat.com>
 <20221022154819.1823133-4-eesposit@redhat.com>
 <62500f94-b95b-1e16-4aa2-f67905fab01a@redhat.com>
From:   Emanuele Giuseppe Esposito <eesposit@redhat.com>
In-Reply-To: <62500f94-b95b-1e16-4aa2-f67905fab01a@redhat.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Precedence: bulk


Am 23/10/2022 um 19:50 schrieb Paolo Bonzini:
> On 10/22/22 17:48, Emanuele Giuseppe Esposito wrote:
>> +static DECLARE_RWSEM(memory_transaction);
> 
> This cannot be global, it must be per-struct kvm.  Otherwise one VM can
> keep the rwsem indefinitely while a second VM hangs in
> KVM_KICK_ALL_RUNNING_VCPUS.
> 
> It can also be changed to an SRCU (with the down_write+up_write sequence
> changed to synchronize_srcu_expedited) which has similar characteristics
> to your use of the rwsem.
> 

Makes sense, but why synchronize_srcu_expedited and not synchronize_srcu?

Thank you,
Emanuele