linux-kernel - Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

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Date:   Thu, 5 Jul 2018 14:41:25 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Raslan, KarimAllah" <karahmed@...zon.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Cc:     "rkrcmar@...hat.com" <rkrcmar@...hat.com>
Subject: Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

On 05/07/2018 14:22, Raslan, KarimAllah wrote:
>> They don't support atomics on double-word data.
> But they support atomics on single words. Of which there are two.
> We don't need atomic updates of the whole 64-bit quantity (a là 
> cmpxchg). Do we strictly need this to be atomic accross the 64-bit?
> 
> Looking at the use cases for "requests":
> 
> kvm_clear_request
> kvm_test_request
> kvm_request_pending
> kvm_check_request
> 
> ... and all of them would still work if the atomicity is only at the 
> word level, right?
> 

Good point!  Then yes, requests can be made 64 bit wide.

Paolo