linux-kernel - Re: [PATCH v2 02/14] KVM: SVM: Free sev_asid

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Message-ID: <YAB7ceKeOdfkDnoA@google.com>
Date:   Thu, 14 Jan 2021 09:12:17 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        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, Borislav Petkov <bp@...e.de>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v2 02/14] KVM: SVM: Free sev_asid_bitmap during init if
 SEV setup fails

On Thu, Jan 14, 2021, Tom Lendacky wrote:
> On 1/13/21 6:36 PM, Sean Christopherson wrote:
> > Free sev_asid_bitmap if the reclaim bitmap allocation fails, othwerise
> > KVM will unnecessarily keep the bitmap when SEV is not fully enabled.
> > 
> > Freeing the page is also necessary to avoid introducing a bug when a
> > future patch eliminates svm_sev_enabled() in favor of using the global
> > 'sev' flag directly.  While sev_hardware_enabled() checks max_sev_asid,
> > which is true even if KVM setup fails, 'sev' will be true if and only
> > if KVM setup fully succeeds.
> > 
> > Fixes: 33af3a7ef9e6 ("KVM: SVM: Reduce WBINVD/DF_FLUSH invocations")
> > Cc: Tom Lendacky <thomas.lendacky@....com>
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> >   arch/x86/kvm/svm/sev.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > index c8ffdbc81709..0eeb6e1b803d 100644
> > --- a/arch/x86/kvm/svm/sev.c
> > +++ b/arch/x86/kvm/svm/sev.c
> > @@ -1274,8 +1274,10 @@ void __init sev_hardware_setup(void)
> >   		goto out;
> >   	sev_reclaim_asid_bitmap = bitmap_zalloc(max_sev_asid, GFP_KERNEL);
> > -	if (!sev_reclaim_asid_bitmap)
> > +	if (!sev_reclaim_asid_bitmap) {
> > +		bitmap_free(sev_asid_bitmap);
> 
> Until that future change, you probably need to do sev_asid_bitmap = NULL
> here to avoid an issue in sev_hardware_teardown() when it tries to free it
> again.

Argh, you're right.  Thanks!