Date: Sat, 17 May 2008 20:53:12 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Rui Paulo <rpaulo@freebsd.org> Cc: freebsd-hackers@freebsd.org, Andriy Gapon <avg@icyb.net.ua> Subject: Re: rdmsr from userspace Message-ID: <20080517175312.GM18958@deviant.kiev.zoral.com.ua> In-Reply-To: <482F1529.5080409@FreeBSD.org> References: <482E93C0.4070802@icyb.net.ua> <482EFBA0.30107@FreeBSD.org> <482F1191.70709@icyb.net.ua> <482F1529.5080409@FreeBSD.org>
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--jva9z9iU4vGix/sz Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat, May 17, 2008 at 06:26:01PM +0100, Rui Paulo wrote: > Andriy Gapon wrote: > >on 17/05/2008 18:37 Rui Paulo said the following: > >>Andriy Gapon wrote: > >>> > >>>It seems that rdmsr instruction can be executed only at the highest=20 > >>>privilege level and thus is not permitted from userland. Maybe we=20 > >>>should provide something like Linux /dev/cpu/msr? > >>>I don't like interface of that device, I think that ioctl approach=20 > >>>would be preferable in this case. > >>>Something like create /dev/cpuN and allow some ioctls on it:=20 > >>>ioctl(cpu_fd, CPU_RDMSR, arg). > >>>What do you think? > >>> > >> > >>While I think this (devcpu) is good for testing and development, I=20 > >>prefer having a device driver to handle that specific MSR than a=20 > >>generic /dev/cpuN where you can issue MSRs. > >>Both for security and reliability reasons. > > > >What about /dev/pci, /dev/io? Aren't they a precedent? >=20 > They are, but, IMHO, we should no longer continue to create this type of= =20 > interfaces. Why ? Are developers some kind of the second-class users ? I would have no opinion on providing /dev/cpu by the loadable module, not compiled into GENERIC. But the interface itself is useful at least for three things: - CPU identification (see x86info or whatever it is called); - CPU tweaking for bugs workaround without patching the kernel; - updating the CPU microcode. None of these is limited to the developers only. I am interested why Stanislav still did not submitted it for inclusion into the base still. Maybe, some other reasons exist. --jva9z9iU4vGix/sz Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAkgvG4gACgkQC3+MBN1Mb4iodgCcCKViPJjwM7qHV/sFSDZOK/zS OQkAoN6vNYhb9CltjRgoBAU3fkNyP4Rt =1Z2a -----END PGP SIGNATURE----- --jva9z9iU4vGix/sz--
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