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

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Date:   Thu, 14 Jan 2021 12:02:19 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Sean Christopherson <seanjc@...gle.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 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, 
should the allocation of the second bitmap fail, until kvm_amd is 
rmmod'ed. Up to you.

Thanks,
Tom

>>> 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!
>