Message-ID: <405DCDA1.3080008@colorfullife.com>
Date: Sun, 21 Mar 2004 18:15:13 +0100
From: Manfred Spraul <manfred@colorfullife.com>
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To: Roland Dreier <roland@topspin.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> <52u10i2lx6.fsf@topspin.com>
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Roland Dreier wrote:

>    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.
>
You are right.
What should happen if there are registered transfers during fork()? Copy 
the pages during the fork() syscall?

--
    Manfred

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