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Date:   Tue, 13 Sep 2022 16:12:04 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Hugh Dickins <hughd@google.com>,
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Subject: Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM
 guest private memory
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On Tue, Sep 13, 2022, Kirill A. Shutemov wrote:
> 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

Hence the comment about 'fallthrough'.  Thanks again!