linux-kernel - Re: RFC v2: post-init-read-only protection for data allocated dynamically

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Message-ID: <361e39e9-517a-2fc2-016c-23f9359fef0a@intel.com>
Date:   Thu, 4 May 2017 10:24:42 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Igor Stoppa <igor.stoppa@...wei.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: RFC v2: post-init-read-only protection for data allocated
 dynamically

On 05/04/2017 07:01 AM, Michal Hocko wrote:
> Just to make my proposal more clear. I suggest the following workflow
> 
> cache = kmem_cache_create(foo, object_size, ..., SLAB_SEAL);
> 
> obj = kmem_cache_alloc(cache, gfp_mask);
> init_obj(obj)
> [more allocations]
> kmem_cache_seal(cache);
> 
> All slab pages belonging to the cache would get write protection. All
> new allocations from this cache would go to new slab pages. Later
> kmem_cache_seal will write protect only those new pages.

Igor, what sizes of objects are you after here, mostly?

I ask because slub, at least, doesn't work at all for objects
>PAGE_SIZE.  It just punts those to the page allocator.  But, you
_could_ still use vmalloc() for those.