Date: Wed, 02 Dec 1998 16:09:08 -0800 From: Mike Smith <mike@smith.net.au> To: Peter Jeremy <peter.jeremy@auss2.alcatel.com.au> Cc: mike@smith.net.au, current@FreeBSD.ORG Subject: Re: sio breakage Message-ID: <199812030009.QAA00645@dingo.cdrom.com> In-Reply-To: Your message of "Wed, 02 Dec 1998 20:26:51 %2B1100." <98Dec2.202617est.40351@border.alcanet.com.au>
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> An alternative approach would be to leave IOPL at 0 and use the I/O > Permission bitmap in the TSS. This allows I/O without allowing > CLI/STI. The disadvantage is that either you have a per-process TSS > (which is expensive in memory), or the TSS needs to be re-written on a > context switch (which is expensive in time). BSDI (at least BSDI 1.1) > used this approach - but the bitmap was system-wide, so enabling an > I/O port for any process enabled it for all processes (which isn't > particularly secure). [And at least on 486's, I/O instructions are > much slower is the IOPB is used instead of IOPL - even slower than > accessing the ISA bus :-(]. For what it's worth, we allow a per-process IO permission bitmap; see i386_set_ioperm. > (*) The need to atomically issue multiple I/O instructions could be > seen to be a justification for this. Hmm, good point. I wonder how common this actually is? -- \\ Sometimes you're ahead, \\ Mike Smith \\ sometimes you're behind. \\ mike@smith.net.au \\ The race is long, and in the \\ msmith@freebsd.org \\ end it's only with yourself. \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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