[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Porting of Guest OS
Ronald G. Minnich wrote: On Fri, 31 Dec 2004, David Hopwood wrote:It should be possible to make it work by using the hypervisor interface equivalents of rdmsr/wrmsr. See section 9.11 of the IA32 architecture manual Volume 3. <http://developer.intel.com/design/pentium4/manuals/index_new.htm> <ftp://download.intel.com/design/Pentium4/manuals/25366814.pdf> interesting. Part of the microcode upgrade process is pointing the CPU at a chunk of memory that it ingests as the new microcode. I found the whole business a bit dicey to think about from ring 1, but I guess it ought to be fine. I really shouldn't post at that time of the morning. First, it should have been obvious that DOM0 only runs on a single CPU, since multiprocessor guests aren't supported yet. Second, the architecture manual only gives sample code for doing the update in real mode; it seems to imply that this will also work from protected mode, but it's not quite clear what the requirements are. Based on the code of the Linux kernel driver: <http://lxr.linux.no/source/arch/i386/kernel/microcode.c#L288> it looks like EAX just has to contain a linear address when Linux is running on bare hardware (the driver casts a pointer in the data segment, which is zero-based, to an unsigned int). In order to use a generic wrmsr hypercall, DOM0 would have to calculate what linear address Xen should use, which although possible (I think), is a horrible layering violation that would depend on implementation details of Xen. It would be much cleaner to either: - add a privileged hypercall specifically to allow DOM0 to update the microcode on all processors (essentially just copy the Linux driver into Xen), - compile the latest microcode into Xen and have it do the update at boot. This would require people to upgrade Xen in order to upgrade the microcode. -- David Hopwood <david.nospam.hopwood@xxxxxxxxxxxxxxxx> ------------------------------------------------------- The SF.Net email is sponsored by: Beat the post-holiday blues Get a FREE limited edition SourceForge.net t-shirt from ThinkGeek. It's fun and FREE -- well, almost....http://www.thinkgeek.com/sfshirt _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/xen-devel
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