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 14:49:26 -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 2:14 PM, Sean Christopherson wrote:

> 
> Where?  I feel like I'm missing something.  The only change to sev_free_vcpu() I
> see is that addition of the rmpupdate(), I don't see any reclaim path.

Clearing of the immutable bit (aka reclaim) is done by the firmware 
after the command was successful. See the section 8.14.2.1 of the 
SEV-SNP spec[1].

   The firmware encrypts the page with the VEK in place. The firmware
   sets the RMP.VMSA of the page to 1. The firmware sets the VMPL
   permissions for the page and transitions the page to Guest-Valid.

The Guest-Valid state means the immutable bit is cleared.  In this case,
the hypervisor just need to make the page shared and that's what the 
sev_free_vcpu() does to ensure that page is transitioned from the 
Guest-Valid to Hypervisor.

[1] https://www.amd.com/system/files/TechDocs/56860.pdf

thanks