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

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Message-ID: <YACYx68nBGOe2ROg@google.com>
Date:   Thu, 14 Jan 2021 11:17:27 -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 1/14/21 11:12 AM, Sean Christopherson wrote:
> > 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")
> 
> Oops, missed this last time... I don't think the Fixes: tag is needed
> anymore unless you don't want the memory consumption of the first bitmap,

If Fixes is viewed as purely a "this needs to be backported", then yes, it
should be dropped.  But, since KVM policy is to backport only patches that are
explicitly tagged with stable@, I like to use to Fixes to create a paper trail
for bug fixes even if the bug is essentially benign.

That being said, I have no objection to dropping it if anyone feels strongly
about not playing fast and loose with Fixes.

> should the allocation of the second bitmap fail, until kvm_amd is rmmod'ed.
> Up to you.