linux-kernel - RE: [PATCH Part2 v6 24/49] KVM: SVM: Add KVM_SEV_SNP_LAUNCH

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Message-ID: <SN6PR12MB27670876B5EA34D00281950F8EB49@SN6PR12MB2767.namprd12.prod.outlook.com>
Date:   Fri, 24 Jun 2022 18:17:45 +0000
From:   "Kalra, Ashish" <Ashish.Kalra@....com>
To:     Peter Gonda <pgonda@...gle.com>
CC:     the arch/x86 maintainers <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
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        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
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        Tony Luck <tony.luck@...el.com>, Marc Orr <marcorr@...gle.com>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Alper Gun <alpergun@...gle.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        "jarkko@...nel.org" <jarkko@...nel.org>
Subject: RE: [PATCH Part2 v6 24/49] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_START
 command

[AMD Official Use Only - General]

>> +static int snp_decommission_context(struct kvm *kvm) {
>> +       struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>> +       struct sev_data_snp_decommission data = {};
>> +       int ret;
>> +
>> +       /* If context is not created then do nothing */
>> +       if (!sev->snp_context)
>> +               return 0;
>> +
>> +       data.gctx_paddr = __sme_pa(sev->snp_context);
>> +       ret = snp_guest_decommission(&data, NULL);

>Do we have a similar race like in sev_unbind_asid() with DEACTIVATE and WBINVD/DF_FLUSH? The SNP_DECOMMISSION spec looks quite similar to DEACTIVATE.

Yes, SNP_DECOMMISION also marks the ASID as invalid and require a WBINVD/DF_FLUSH before the ASID is re-used/re-cycled, so we need to prevent against
DECOMMISION and ASID re-cycling happening at the same time. Can reuse the same RWSEM (sev_deactivate_lock) here too.

Thanks,
Ashish

> +       if (WARN_ONCE(ret, "failed to release guest context"))
> +               return ret;
> +
> +       /* free the context page now */
> +       snp_free_firmware_page(sev->snp_context);
> +       sev->snp_context = NULL;
> +
> +       return 0;
> +}
> +
>  void sev_vm_destroy(struct kvm *kvm)
>  {
>         struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;