linux-kernel - Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

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Date:   Thu, 16 Feb 2023 10:41:14 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...nel.org>,
        Chao Peng <chao.p.peng@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, qemu-devel@...gnu.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Arnd Bergmann <arnd@...db.de>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Miaohe Lin <linmiaohe@...wei.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, aarcange@...hat.com, ddutile@...hat.com,
        dhildenb@...hat.com, Quentin Perret <qperret@...gle.com>,
        tabba@...gle.com, Michael Roth <michael.roth@....com>,
        mhocko@...e.com, wei.w.wang@...el.com
Subject: Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

On 16.02.23 06:13, Mike Rapoport wrote:
> Hi,
> 
> On Fri, Dec 02, 2022 at 02:13:38PM +0800, Chao Peng wrote:
>> This patch series implements KVM guest private memory for confidential
>> computing scenarios like Intel TDX[1]. If a TDX host accesses
>> TDX-protected guest memory, machine check can happen which can further
>> crash the running host system, this is terrible for multi-tenant
>> configurations. The host accesses include those from KVM userspace like
>> QEMU. This series addresses KVM userspace induced crash by introducing
>> new mm and KVM interfaces so KVM userspace can still manage guest memory
>> via a fd-based approach, but it can never access the guest memory
>> content.
> 
> Sorry for jumping late.
> 
> Unless I'm missing something, hibernation will also cause an machine check
> when there is TDX-protected memory in the system. When the hibernation
> creates memory snapshot it essentially walks all physical pages and saves
> their contents, so for TDX memory this will trigger machine check, right?

I recall bringing that up in the past (also memory access due to kdump, 
/prov/kcore) and was told that the main focus for now is preventing 
unprivileged users from crashing the system, that is, not mapping such 
memory into user space (e.g., QEMU). In the long run, we'll want to 
handle such pages also properly in the other events where the kernel 
might access them.

-- 
Thanks,

David / dhildenb