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

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Date:   Fri, 13 Jan 2023 17:00:24 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Michael Roth <michael.roth@....com>
Cc:     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, seanjc@...gle.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 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...?

And what's the story with supporting UPM with SEV{,-ES} guests?

In general, this text needs more background and why this is being done.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette