Date: Wed, 26 Jul 2000 15:58:27 -0400 (EDT) From: Luoqi Chen <luoqi@watermarkgroup.com> To: current@freebsd.org Subject: page fault at write-only mmapped address Message-ID: <200007261958.e6QJwRT13115@lor.watermarkgroup.com>
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Because there is no write-only hardware page protection on ia32, a write-only page fault is handled just like a read/write one. But the mi vm layer distinguishes between the write-only and the read/write protections, so if the fault takes place in a write-only region, the vm layer would think that the write-only operation is trying to read from a write-only address and violates the page protection. As a consequence, if you want to use the sound device in mmapped mode, you'll have to map the playback buffer read/write instead of write-only. I'd like to reverse the way read/write and write-only page faults are handled, i.e., handle both of them like a write-only fault. Does anyone know any reason why I shouldn't do that? I'm currently running a kernel with this modification and I have seen no ill-effect so far. -lq To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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