linux-kernel - Re: [PATCH 1/2] KVM: SVM: free sev_*asid

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Date:   Wed, 12 Apr 2023 16:52:23 +0200
From:   Aleksandr Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
To:     Zhi Wang <zhi.wang.linux@...il.com>
Cc:     pbonzini@...hat.com, Sean Christopherson <seanjc@...gle.com>,
        Stéphane Graber <stgraber@...ntu.com>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: SVM: free sev_*asid_bitmap init if SEV init fails

On Tue, Apr 11, 2023 at 9:47 PM Zhi Wang <zhi.wang.linux@...il.com> wrote:
>
> On Tue,  4 Apr 2023 14:26:51 +0200
> Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com> wrote:
>
> > If misc_cg_set_capacity() fails for some reason then we have
> > a memleak for sev_reclaim_asid_bitmap/sev_asid_bitmap. It's
> > not a case right now, because misc_cg_set_capacity() just can't
> > fail and check inside it is always successful.
> >
> > But let's fix that for code consistency.
> >
> > Cc: Sean Christopherson <seanjc@...gle.com>
> > Cc: Paolo Bonzini <pbonzini@...hat.com>
> > Cc: Stéphane Graber <stgraber@...ntu.com>
> > Cc: kvm@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
> > ---
> >  arch/x86/kvm/svm/sev.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > index c25aeb550cd9..a42536a0681a 100644
> > --- a/arch/x86/kvm/svm/sev.c
> > +++ b/arch/x86/kvm/svm/sev.c
> > @@ -2213,8 +2213,13 @@ void __init sev_hardware_setup(void)
> >       }
> >
> >       sev_asid_count = max_sev_asid - min_sev_asid + 1;
> > -     if (misc_cg_set_capacity(MISC_CG_RES_SEV, sev_asid_count))
> > +     if (misc_cg_set_capacity(MISC_CG_RES_SEV, sev_asid_count)) {
> > +             bitmap_free(sev_reclaim_asid_bitmap);
> > +             sev_reclaim_asid_bitmap = NULL;
> > +             bitmap_free(sev_asid_bitmap);
> > +             sev_asid_bitmap = NULL;
> >               goto out;
> > +     }
> >
> >       pr_info("SEV supported: %u ASIDs\n", sev_asid_count);
> >       sev_supported = true;
>
> It would be nice that another case can also be fixed:
>
>         sev_es_asid_count = min_sev_asid - 1;
>         if (misc_cg_set_capacity(MISC_CG_RES_SEV_ES, sev_es_asid_count))
>                 goto out; /* <----HERE */

Nope.

There is no leak. Because when we are at this point then sev_supported
= true and everything is fine.

>
> Maybe it would be a good idea to factor out an common error handling path.