linux-kernel - Re: [PATCH] KVM: SEV: improve the code readability for ASID management

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Message-ID: <71a905a1-0a6f-0d7a-f8fe-237b9e5af05c@redhat.com>
Date:   Mon, 2 Aug 2021 18:52:54 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Marc Orr <marcorr@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Alper Gun <alpergun@...gle.com>,
        Dionna Glaze <dionnaglaze@...gle.com>,
        Vipin Sharma <vipinsh@...gle.com>
Subject: Re: [PATCH] KVM: SEV: improve the code readability for ASID
 management

On 02/08/21 18:17, Sean Christopherson wrote:
> 
> Rather than adjusting the bitmap index, what about simply umping the bitmap size?
> IIRC, current CPUs have 512 ASIDs, counting ASID 0, i.e. bumping the size won't
> consume any additional memory.  And if it does, the cost is 8 bytes...
> 
> It'd be a bigger refactoring, but it should completely eliminate the mod-by-1
> shenanigans, e.g. a partial patch could look like

This is also okay by me if Mingwei agrees, of course.  I have already 
queued his patch, but I can replace it with one using a nr_asids-sized 
bitmap too.

Paolo