Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Feedback-ID: ie3994620:Fastmail
Date:   Tue, 13 Sep 2022 19:00:46 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Sean Christopherson <seanjc@google.com>
Cc:     "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Hugh Dickins <hughd@google.com>,
        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-api@vger.kernel.org,
        linux-doc@vger.kernel.org, qemu-devel@nongnu.org,
        linux-kselftest@vger.kernel.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>,
        x86@kernel.org, "H . Peter Anvin" <hpa@zytor.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>, 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>,
        Michael Roth <michael.roth@amd.com>, mhocko@suse.com,
        Muchun Song <songmuchun@bytedance.com>,
        "Gupta, Pankaj" <pankaj.gupta@amd.com>,
        Elena Reshetova <elena.reshetova@intel.com>
Subject: Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM
 guest private memory
Message-ID: <20220913160046.rkz7uh6cpwy6wyzg@box.shutemov.name>
References: <ff5c5b97-acdf-9745-ebe5-c6609dd6322e@google.com>
 <20220818132421.6xmjqduempmxnnu2@box>
 <c6ccbb96-5849-2e2f-3b49-4ea711af525d@google.com>
 <20220820002700.6yflrxklmpsavdzi@box.shutemov.name>
 <c194262b-b634-4baf-abf0-dc727e8f1d7@google.com>
 <20220831142439.65q2gi4g2d2z4ofh@box.shutemov.name>
 <20220908011037.ez2cdorthqxkerwk@box.shutemov.name>
 <YyBQ+wzPtGwwRB/U@google.com>
 <20220913132821.3ch5cv3rgdxqgz3i@box.shutemov.name>
 <YyCZZSyCrwXLLCD9@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <YyCZZSyCrwXLLCD9@google.com>
Precedence: bulk

On Tue, Sep 13, 2022 at 02:53:25PM +0000, Sean Christopherson wrote:
> > > Switching topics, what actually prevents mmapp() on the shim?  I tried to follow,
> > > but I don't know these areas well enough.
> > 
> > It has no f_op->mmap, so mmap() will fail with -ENODEV. See do_mmap().
> > (I did not read the switch statement correctly at first. Note there are
> > two 'fallthrough' there.)
> 
> Ah, validate_mmap_request().  Thought not implementing ->mmap() was the key, but
> couldn't find the actual check.

validate_mmap_request() is in mm/nommu.c which is not relevant for real
computers.

I was talking about this check:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/mmap.c#n1495

-- 
  Kiryl Shutsemau / Kirill A. Shutemov