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On my laptop running at 2.4GHz, if I run a VM where tsc calibration using pmtimer will fail presuming a broken pmtimer, it takes ~51 seconds to do so (as measured with the stopwatch on my phone), with a tsc delta of 0x1cd1c85300, or around 125 billion cycles. If instead of trying to wait for 5-200ms to show up on the pmtimer, we try to wait for 5-200us, it decides it's broken in ~0x2626aa0 TSCs, aka ~2.4 million cycles, or more or less instantly. Additionally, this reading the pmtimer was returning 0xffffffff anyway, and that's obviously an invalid return. I've added a check for that and 0 so we don't bother waiting for the test if what we're seeing is dead pins with no response at all. If "debug" includes "pmtimer", you will see one of the following three outcomes. If pmtimer gives all 0 or all 1 bits, you will see: pmtimer: 0xffffff bad_reads: 1 pmtimer: 0xffffff bad_reads: 2 pmtimer: 0xffffff bad_reads: 3 pmtimer: 0xffffff bad_reads: 4 pmtimer: 0xffffff bad_reads: 5 pmtimer: 0xffffff bad_reads: 6 pmtimer: 0xffffff bad_reads: 7 pmtimer: 0xffffff bad_reads: 8 pmtimer: 0xffffff bad_reads: 9 pmtimer: 0xffffff bad_reads: 10 timer is broken; giving up. This outcome was tested using qemu+kvm with UEFI (OVMF) firmware and these options: -machine pc-q35-2.10 -cpu Broadwell-noTSX If pmtimer gives any other bit patterns but is not actually marching forward fast enough to use for clock calibration, you will see: pmtimer delta is 0x0 (1904 iterations) tsc delta is implausible: 0x2626aa0 This outcome was tested using GRUB patched to not ignore bad reads using qemu+kvm with UEFI (OVMF) firmware, and these options: -machine pc-q35-2.10 -cpu Broadwell-noTSX If pmtimer actually works, you'll see something like: pmtimer delta is 0xdff tsc delta is 0x278756 This outcome was tested using qemu+kvm with UEFI (OVMF) firmware, and these options: -machine pc-i440fx-2.4 -cpu Broadwell-noTSX I've also tested this outcome on a real Intel Xeon E3-1275v3 on an Intel Server Board S1200V3RPS using the SDV.RP.B8 "Release" build here: https://www.intel.com/content/www/us/en/download/674448/firmware-update-for-the-intel-server-board-s1200rp-uefi-development-kit-release-vb8.html Signed-off-by: Peter Jones <pjones@redhat.com> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com> Signed-off-by: Robbie Harwood <rharwood@redhat.com> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This is GRUB 2, the second version of the GRand Unified Bootloader. GRUB 2 is rewritten from scratch to make GNU GRUB cleaner, safer, more robust, more powerful, and more portable. See the file NEWS for a description of recent changes to GRUB 2. See the file INSTALL for instructions on how to build and install the GRUB 2 data and program files. See the file MAINTAINERS for information about the GRUB maintainers, etc. If you found a security vulnerability in the GRUB please check the SECURITY file to get more information how to properly report this kind of bugs to the maintainers. Please visit the official web page of GRUB 2, for more information. The URL is <http://www.gnu.org/software/grub/grub.html>. More extensive documentation is available in the Info manual, accessible using 'info grub' after building and installing GRUB 2. There are a number of important user-visible differences from the first version of GRUB, now known as GRUB Legacy. For a summary, please see: info grub Introduction 'Changes from GRUB Legacy'