To: Manfred Spraul <manfred@colorfullife.com>
Cc: Eli Cohen <mlxk@mellanox.co.il>, linux-kernel@vger.kernel.org
Subject: Re: locking user space memory in kernel
References: <405D7D2F.9050507@colorfullife.com>
From: Roland Dreier <roland@topspin.com>
Date: 21 Mar 2004 08:40:37 -0800
In-Reply-To: <405D7D2F.9050507@colorfullife.com>
Message-ID: <52u10i2lx6.fsf@topspin.com>
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    Manfred> I think just get_user_pages() should be sufficient: the
    Manfred> pages won't be swapped out. You don't need to set
    Manfred> VM_LOCKED in vma->vm_flags to prevent the swap out. In
    Manfred> the worst case, the pte is cleared a that will cause a
    Manfred> soft page fault, but the physical address won't
    Manfred> change. Multiple get_user_pages() calls on overlapping
    Manfred> regions are ok, the page count is an atomic_t, at least
    Manfred> 24-bit large.

There is one case that we ran into where the physical address can
change: if a process does a fork() and then triggers COW.

 - Roland

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