linux-kernel - Re: [PATCH Part2 RFC v4 26/40] KVM: SVM: Add KVM_SEV_SNP_LAUNCH

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Date:   Mon, 19 Jul 2021 13:29:58 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>, tony.luck@...el.com,
        npmccallum@...hat.com, brijesh.ksingh@...il.com
Subject: Re: [PATCH Part2 RFC v4 26/40] KVM: SVM: Add
 KVM_SEV_SNP_LAUNCH_FINISH command



On 7/19/21 11:54 AM, Sean Christopherson wrote:
>> As I said in previous comments that by default all the memory is in the
>> hypervisor state. if the rmpupdate() failed that means nothing is changed in
>> the RMP and there is no need to reclaim. The reclaim is required only if the
>> pages are assigned in the RMP table.
> 
> I wasn't referring to RMPUPDATE failing here (or anywhere).  This is the vCPU free
> path, which I think means the svm->vmsa page was successfully updated in the RMP
> during LAUNCH_UPDATE.  snp_launch_update_vmsa() goes through snp_page_reclaim()
> on LAUNCH_UPDATE failure, whereas this happy path does not.  Is there some other
> transition during teardown that obviastes the need for reclaim?  If so, a comment
> to explain that would be very helpful.
> 

In this patch, the sev_free_vcpu() hunk takes care of reclaiming the 
vmsa pages before releasing it. I think it will make it more obvious 
after I add a helper so that we don't depend on user reading the comment 
block to see what its doing.

-Brijesh