linux-kernel - Re: [PATCH 7/9] Pmalloc Rare Write: modify selected pools

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Message-ID: <20180424115050.GD26636@bombadil.infradead.org>
Date:   Tue, 24 Apr 2018 04:50:50 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Igor Stoppa <igor.stoppa@...il.com>
Cc:     keescook@...omium.org, paul@...l-moore.com, sds@...ho.nsa.gov,
        mhocko@...nel.org, corbet@....net, labbott@...hat.com,
        linux-cc=david@...morbit.com, --cc=rppt@...ux.vnet.ibm.com,
        --security-module@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        Igor Stoppa <igor.stoppa@...wei.com>,
        Carlos Chinea Perez <carlos.chinea.perez@...wei.com>,
        Remi Denis Courmont <remi.denis.courmont@...wei.com>
Subject: Re: [PATCH 7/9] Pmalloc Rare Write: modify selected pools

On Mon, Apr 23, 2018 at 04:54:56PM +0400, Igor Stoppa wrote:
> While the vanilla version of pmalloc provides support for permanently
> transitioning between writable and read-only of a memory pool, this
> patch seeks to support a separate class of data, which would still
> benefit from write protection, most of the time, but it still needs to
> be modifiable. Maybe very seldom, but still cannot be permanently marked
> as read-only.

This seems like a horrible idea that basically makes this feature useless.
I would say the right way to do this is to have:

struct modifiable_data {
	struct immutable_data *d;
	...
};

Then allocate a new pool, change d and destroy the old pool.