linux-kernel - Re: [PATCH 3/4] KVM: introduce memory transaction semaphore

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Message-ID: <fba8e829-0d28-8f4d-a8ce-84d533009eb9@redhat.com>
Date:   Mon, 24 Oct 2022 14:57:33 +0200
From:   Emanuele Giuseppe Esposito <eesposit@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Cc:     Jonathan Corbet <corbet@....net>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] KVM: introduce memory transaction semaphore



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