Re: [PATCH v2 02/14] KVM: SVM: Free sev_asid_bitmap during init if SEV setup fails

Tom Lendacky
2021-01-14T18:03:23Z

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@amd.com>
>>> Signed-off-by: Sean Christopherson <seanjc@google.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!
>