Date: Tue, 14 Jun 2005 15:30:42 -0600 From: Scott Long <scottl@samsco.org> To: John-Mark Gurney <gurney_j@resnet.uoregon.edu> Cc: freebsd-hackers <freebsd-hackers@freebsd.org>, Aziz Kezzou <french.linuxian@gmail.com>, freebsd-net <freebsd-net@freebsd.org> Subject: Re: FreeBSD Memory Management questions ? Message-ID: <42AF4C82.7070306@samsco.org> In-Reply-To: <20050614212214.GK742@funkthat.com> References: <37273927050614012154fdb80b@mail.gmail.com> <20050614212214.GK742@funkthat.com>
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John-Mark Gurney wrote: > Aziz Kezzou wrote this message on Tue, Jun 14, 2005 at 04:21 -0400: > >>I have two questions concerning FreeBSD Memory management : >> >>1 - Right now to access the memory address space of a user process >>from kernel mode, I only have to set, on x86 systems, the register CR3 >>to the right value. How can I do that on other architectures ? is >>there an architecture-independant way of doing that ? >> >>2- I have noticed that while in kernel mode the value of CR3 is equal >>to that of the user process beeing interrupted. Doesn't the kernel >>supposed to have its "own" page-directory, i.e it's own CR3 value ? >>or is kernel virtual address resolution does not go through CR3 at >>all ? > > > You should be using copyin(9)/copyout(9) instead of playing around with > CR3 directly... or fuword(9)/suword(9)... This provides a platform > independant way of accessing user's memory (for the current running > process)... > Not to mention that setting CR3, or whatever on other platforms, doesn't handle accessing pages that have been swapped out. That's the real magic that copyin/copyout does. Scott
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