linux-kernel - Re: [RFCv2 15/16] KVM: Unmap protected pages from direct mapping

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Message-ID: <2fe169d4-ce99-1f30-2fea-89d524fe05a8@amd.com>
Date:   Mon, 26 Oct 2020 14:55:20 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     David Hildenbrand <david@...hat.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Mike Rapoport <rppt@...ux.ibm.com>
Cc:     David Rientjes <rientjes@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Will Drewry <wad@...omium.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>,
        Liran Alon <liran.alon@...cle.com>,
        Mike Rapoport <rppt@...nel.org>, x86@...nel.org,
        kvm@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [RFCv2 15/16] KVM: Unmap protected pages from direct mapping

On 10/20/20 7:18 AM, David Hildenbrand wrote:
> On 20.10.20 08:18, Kirill A. Shutemov wrote:
>> If the protected memory feature enabled, unmap guest memory from
>> kernel's direct mappings.
> 
> Gah, ugly. I guess this also defeats compaction, swapping, ... oh gosh.
> As if all of the encrypted VM implementations didn't bring us enough
> ugliness already (SEV extensions also don't support reboots, but can at
> least kexec() IIRC).

SEV does support reboot. SEV-ES using Qemu doesn't support reboot because
of the way Qemu resets the vCPU state. If Qemu could relaunch the guest
through the SEV APIs to reset the vCPU state, then a "reboot" would be
possible.

SEV does support kexec, SEV-ES does not at the moment.

Thanks,
Tom

> 
> Something similar is done with secretmem [1]. And people don't seem to
> like fragmenting the direct mapping (including me).
> 
> [1] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.kernel.org%2Fr%2F20200924132904.1391-1-rppt%40kernel.org&amp;data=04%7C01%7Cthomas.lendacky%40amd.com%7Cb98a5033da37432131b508d874f25194%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637387931403890525%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=BzC%2FeIyOau7BORuUY%2BaiRzYZ%2BOAHANvBDcmV9hpkrts%3D&amp;reserved=0
>