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Date: Wed, 27 Apr 2016 17:57:30 +0200
From: Andrea Arcangeli <aarcange@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/1] mm: thp: kvm: fix memory corruption in
 KVM with THP enabled
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To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, qemu-devel@nongnu.org, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, "Li, Liang Z" <liang.z.li@intel.com>, Amit Shah <amit.shah@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>

On Wed, Apr 27, 2016 at 06:18:34PM +0300, Kirill A. Shutemov wrote:
> Okay, I see.
> 
> But do we really want to make PageTransCompoundMap() visiable beyond KVM
> code? It looks like too KVM-specific.

Any other secondary MMU notifier manager (KVM is just one of the many
MMU notifier users) will need the same information if it doesn't want
to run a flood of get_user_pages_fast and it can support multiple
granularity in the secondary MMU mappings, so I think it is justified
to be exposed not just to KVM.

The other option would be to move transparent_hugepage_adjust to
mm/huge_memory.c but that currently has all kind of KVM data
structures in it, so it's definitely not a cut-and-paste work, so I
couldn't do a fix as cleaner as this one for 4.6.