linux-kernel - Re: [stable 5.10 PATCH] mm: khugepaged: skip huge page collapse for special files

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Message-ID: <YYOXdQbeNGHb0ewM@kroah.com>
Date:   Thu, 4 Nov 2021 09:19:01 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Yang Shi <shy828301@...il.com>
Cc:     hughd@...gle.com, sunhao.th@...il.com, willy@...radead.org,
        kirill.shutemov@...ux.intel.com, songliubraving@...com,
        andrea.righi@...onical.com, akpm@...ux-foundation.org,
        stable@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [stable 5.10 PATCH] mm: khugepaged: skip huge page collapse for
 special files

On Wed, Nov 03, 2021 at 01:22:58PM -0700, Yang Shi wrote:
> commit a4aeaa06d45e90f9b279f0b09de84bd00006e733 upstream.
> 
> The read-only THP for filesystems will collapse THP for files opened
> readonly and mapped with VM_EXEC.  The intended usecase is to avoid TLB
> misses for large text segments.  But it doesn't restrict the file types
> so a THP could be collapsed for a non-regular file, for example, block
> device, if it is opened readonly and mapped with EXEC permission.  This
> may cause bugs, like [1] and [2].
> 
> This is definitely not the intended usecase, so just collapse THP for
> regular files in order to close the attack surface.
> 
> [shy828301@...il.com: fix vm_file check [3]]

Now queued up, thanks.

greg k-h