Date:   Tue, 23 Nov 2021 15:36:35 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Borislav Petkov <bp@alien8.de>
Cc:     Dave Hansen <dave.hansen@intel.com>,
        Brijesh Singh <brijesh.singh@amd.com>,
        Peter Gonda <pgonda@google.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-coco@lists.linux.dev, linux-mm@kvack.org,
        linux-crypto@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
        Tom Lendacky <Thomas.Lendacky@amd.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ard Biesheuvel <ardb@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Sergio Lopez <slp@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Dov Murik <dovmurik@linux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
        Michael Roth <michael.roth@amd.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Andi Kleen <ak@linux.intel.com>, tony.luck@intel.com,
        marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com
Subject: Re: [PATCH Part2 v5 00/45] Add AMD Secure Nested Paging (SEV-SNP)
 Hypervisor Support
Message-ID: <YZ0KgymKvLC2HcIk@google.com>
References: <20210820155918.7518-1-brijesh.singh@amd.com>
 <CAMkAt6o0ySn1=iLYsH0LCnNARrUbfaS0cvtxB__y_d+Q6DUzfA@mail.gmail.com>
 <daf5066b-e89b-d377-ed8a-9338f1a04c0d@amd.com>
 <d673f082-9023-dafb-e42e-eab32a3ddd0c@intel.com>
 <f15597a0-e7e0-0a57-39fd-20715abddc7f@amd.com>
 <5f3b3aab-9ec2-c489-eefd-9136874762ee@intel.com>
 <d83e6668-bec4-8d1f-7f8a-085829146846@amd.com>
 <38282b0c-7eb5-6a91-df19-2f4cfa8549ce@intel.com>
 <YZyVx38L6gf689zq@zn.tnic>
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On Tue, Nov 23, 2021, Borislav Petkov wrote:
> On Mon, Nov 22, 2021 at 02:51:35PM -0800, Dave Hansen wrote:
> > By "supporting", do you mean doing something functional?  I don't really
> > care if ptrace() to guest private memory returns -EINVAL or whatever.
> > The most important thing is not crashing the host.
> > 
> > Also, as Sean mentioned, this isn't really about ptrace() itself.  It's
> > really about ensuring that no kernel or devices accesses to guest
> > private memory can induce bad behavior.
> 
> I keep repeating this suggestion of mine that we should treat
> guest-private pages as hw-poisoned pages which have experienced a
> uncorrectable error in the past.
> 
> mm already knows how to stay away from those.

Kirill posted a few RFCs that did exactly that.  It's definitely a viable approach,
but it's a bit of a dead end, e.g. doesn't help solve page migration, is limited to
struct page, doesn't capture which KVM guest owns the memory, etc...

https://lore.kernel.org/kvm/20210416154106.23721-1-kirill.shutemov@linux.intel.com/