Date: Sun, 18 May 2008 19:35:44 +0100 From: Rui Paulo <rpaulo@FreeBSD.org> To: Mike Meyer <mwm-keyword-freebsdhackers2.e313df@mired.org> Cc: freebsd-hackers@freebsd.org Subject: Re: rdmsr from userspace Message-ID: <48307700.70304@FreeBSD.org> In-Reply-To: <20080518140650.2691af1c@bhuda.mired.org> References: <482E93C0.4070802@icyb.net.ua> <20080517133037.3a3935db@bhuda.mired.org> <48305044.7000007@FreeBSD.org> <20080518140650.2691af1c@bhuda.mired.org>
next in thread | previous in thread | raw e-mail | index | archive | help
Mike Meyer wrote: > On Sun, 18 May 2008 16:50:28 +0100 > Rui Paulo <rpaulo@FreeBSD.org> wrote: > >> Mike Meyer wrote: >>> On Sat, 17 May 2008 11:13:52 +0300 >>> Andriy Gapon <avg@icyb.net.ua> wrote: >>>> It seems that rdmsr instruction can be executed only at the highest >>>> privilege level and thus is not permitted from userland. Maybe we should >>>> provide something like Linux /dev/cpu/msr? >>>> I don't like interface of that device, I think that ioctl approach would >>>> be preferable in this case. >>>> Something like create /dev/cpuN and allow some ioctls on it: >>>> ioctl(cpu_fd, CPU_RDMSR, arg). >>>> What do you think? >>> Ok, this points directly at a question I've been wondering about, but >>> haven't been able to find an answer in the google. >>> >>> I've been mucking about with general access to sysctl's (a sysctl >>> plugin for gkrellm, and a python module for accessing sysctls), and >>> with that hammer in my hand, the nail for this problem is obviously a >>> dev.cpu.#.msr sysctl. >> How can you request a rdmsr within the sysctl tree? I don't think sysctl >> is appropriate here either. > > Reading (or writing) a sysctl mib can trigger a sysctl handler, which > can do pretty much anything. In particular, there are already examples > in the kernel where sysctl handlers use devices that don't have /dev > entries to get & set their values. Look through kern/kern_cpu.c and > i386/cpufreq/p4tcc.c to see the two ends of that kind of > connection. In fact, the cpu frequency sysctls would seem to be an > excellent model for something like the msr. > > ioctl, open+read/write, sysctl - they're all just interfaces to kernel > handlers. > > <mike Yes, sure, but who do you select the MSR you want to read or write? dev.cpu.N.<insert MSR number in hexadecimal here> ? I'll have to think about whether or not I like this interface. Regards, -- Rui Paulo
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?48307700.70304>