linux-kernel - Re: [PATCH RFC v7 07/64] KVM: SEV: Handle KVM_HC_MAP_GPA

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Date:   Fri, 13 Jan 2023 16:17:30 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Michael Roth <michael.roth@....com>, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, pbonzini@...hat.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, luto@...nel.org,
        dave.hansen@...ux.intel.com, slp@...hat.com, pgonda@...gle.com,
        peterz@...radead.org, srinivas.pandruvada@...ux.intel.com,
        rientjes@...gle.com, dovmurik@...ux.ibm.com, tobin@....com,
        vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
        dgilbert@...hat.com, jarkko@...nel.org, ashish.kalra@....com,
        harald@...fian.com, Nikunj A Dadhania <nikunj@....com>
Subject: Re: [PATCH RFC v7 07/64] KVM: SEV: Handle KVM_HC_MAP_GPA_RANGE
 hypercall

On Fri, Jan 13, 2023, Borislav Petkov wrote:
> On Wed, Dec 14, 2022 at 01:39:59PM -0600, Michael Roth wrote:
> > From: Nikunj A Dadhania <nikunj@....com>
> > 
> > KVM_HC_MAP_GPA_RANGE hypercall is used by the SEV guest to notify a
> > change in the page encryption status to the hypervisor.
> > 
> > The hypercall exits to userspace with KVM_EXIT_HYPERCALL exit code,
> > currently this is used for explicit memory conversion between
> > shared/private for memfd based private memory.
> 
> So Tom and I spent a while to figure out what this is doing...
> 
> Please explain in more detail what that is. Like the hypercall gets ignored for
> memslots which cannot be private...?

Don't bother, just drop the patch.  It's perfectly legal for userspace to create
the private memslot in response to a guest request.