Hello! I would like to ask about a certain thing closely related to the kernel's Microcode Update Driver.
Some new features of CPUs (namely TSX/HLE) have caused many problems in the past (Intel's Haswell) and still continue to be a bleeding edge technology especially when used with not yet well tested software [1][2][3]. I thought it would be very handy to be able to temporarily disable unwanted features of the CPU from the kernel cmdline level. So that underlying libraries and programs do not know they are available, and fallback to standard code. I was in the middle of creating a patch for the disable_cpu_features= kernel parameter when I realized that ignoring them just in the kernel will not solve the problem. Unfortunately glibc does not depend on the CPU flags reported by the kernel, but by itself queries the CPU directly for its features [4]. And so can any other user-space program. It seems the only reliable system-wide solution is to force a CPU microcode update. And here comes my question, as I have no experience in this area: Would it be possible to apply only partial (CPU flags bits) microcode update? Or extract the whole thing, change the requested flags (and the checksum), and re-apply it? Is such thing even possible? And would it be a reasonable thing to do (maybe the rest of the microcode would break badly without the factory flags set)? What do you think? Thank you for any tips on this topic. [1] glibc hardware lock elision issues: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=800574 [2] https://lists.debian.org/debian-glibc/2014/09/msg00076.html Henrique de Moraes Holschuh <[email protected]>: "I recommend that lock elision support in glibc should be disabled for Debian jessie. This thing doesn't look nearly stable enough in glibc 2.19, and any bugs it might cause *will be subtle*." [3] nvidia proprietary driver's hardware lock elision bug: https://devtalk.nvidia.com/default/topic/893325/newest-and-beta-linux-driver-causing-segmentation-fault-core-dumped-on-all-skylake-platforms/ [4] https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/x86_64/multiarch/init-arch.h;hb=78bd7499af46d739ce94410eaeea006e874ca9e5#l175 (ex. line 175) Best Regards, Piotr Dąbrowski -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
