linux-kernel - Re: [PATCH 1/1] mm: thp: kvm: fix memory corruption in KVM with THP enabled

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Message-ID: <20160427155730.GB11700@redhat.com>
Date:	Wed, 27 Apr 2016 17:57:30 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	qemu-devel@...gnu.org,
	"Dr. David Alan Gilbert" <dgilbert@...hat.com>,
	"Li, Liang Z" <liang.z.li@...el.com>,
	Amit Shah <amit.shah@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 1/1] mm: thp: kvm: fix memory corruption in KVM with THP
 enabled

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.