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

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Message-ID: <CAL715WKVZqHG0sJhTn-ebJKjdj5pUQedL9kJjVRWMWoZGbzHFg@mail.gmail.com>
Date:   Mon, 2 Aug 2021 10:25:38 -0700
From:   Mingwei Zhang <mizhang@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm <kvm@...r.kernel.org>,
        LKML <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

Hi Paolo,

Thanks. I think Sean's suggestion makes sense. I will update it with
that one and remove the 'fixes' line.

Regards
-Mingwei

On Mon, Aug 2, 2021 at 9:53 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> 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
>