Date:   Wed, 25 Jan 2023 00:20:26 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Liam Merwick <liam.merwick@oracle.com>
Cc:     Chao Peng <chao.p.peng@linux.intel.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-api@vger.kernel.org, linux-doc@vger.kernel.org,
        qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Arnd Bergmann <arnd@arndb.de>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        Miaohe Lin <linmiaohe@huawei.com>, x86@kernel.org,
        "H . Peter Anvin" <hpa@zytor.com>, Hugh Dickins <hughd@google.com>,
        Jeff Layton <jlayton@kernel.org>,
        "J . Bruce Fields" <bfields@fieldses.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>, Mike Rapoport <rppt@kernel.org>,
        Steven Price <steven.price@arm.com>,
        "Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
        Vlastimil Babka <vbabka@suse.cz>,
        Vishal Annapurve <vannapurve@google.com>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com,
        ak@linux.intel.com, david@redhat.com, aarcange@redhat.com,
        ddutile@redhat.com, dhildenb@redhat.com,
        Quentin Perret <qperret@google.com>, tabba@google.com,
        Michael Roth <michael.roth@amd.com>, mhocko@suse.com,
        wei.w.wang@intel.com
Subject: Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM
Message-ID: <Y9B1yiRR8DpANAEo@google.com>
References: <20221202061347.1070246-1-chao.p.peng@linux.intel.com>
 <Y8H5Z3e4hZkFxAVS@google.com>
 <48953bf2-cee9-f818-dc50-5fb5b9b410bf@oracle.com>
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In-Reply-To: <48953bf2-cee9-f818-dc50-5fb5b9b410bf@oracle.com>
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On Tue, Jan 24, 2023, Liam Merwick wrote:
> On 14/01/2023 00:37, Sean Christopherson wrote:
> > On Fri, Dec 02, 2022, 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.
> > > 
> > > The patch series touches both core mm and KVM code. I appreciate
> > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > > reviews are always welcome.
> > >    - 01: mm change, target for mm tree
> > >    - 02-09: KVM change, target for KVM tree
> > 
> > A version with all of my feedback, plus reworked versions of Vishal's selftest,
> > is available here:
> > 
> >    git@github.com:sean-jc/linux.git x86/upm_base_support
> > 
> > It compiles and passes the selftest, but it's otherwise barely tested.  There are
> > a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> > a WIP.
> > 
> 
> When running LTP (https://github.com/linux-test-project/ltp) on the v10
> bits (and also with Sean's branch above) I encounter the following NULL
> pointer dereference with testcases/kernel/syscalls/madvise/madvise01
> (100% reproducible).
> 
> It appears that in restrictedmem_error_page() inode->i_mapping->private_data
> is NULL
> in the list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list)
> but I don't know why.

Kirill, can you take a look?  Or pass the buck to someone who can? :-)