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[ Upstream commit e1f65b0d70e9e5c80e15105cd96fa00174d7c436 ] It seems with some NICs supported by the e1000e driver a SYSTIM reading may occasionally be few microseconds before the previous reading and if enabled also pass e1000e_sanitize_systim() without reaching the maximum number of rereads, even if the function is modified to check three consecutive readings (i.e. it doesn't look like a double read error). This causes an underflow in the timecounter and the PHC time jumps hours ahead. This was observed on 82574, I217 and I219. The fastest way to reproduce it is to run a program that continuously calls the PTP_SYS_OFFSET ioctl on the PHC. Modify e1000e_phc_gettime() to use timecounter_cyc2time() instead of timecounter_read() in order to allow non-monotonic SYSTIM readings and prevent the PHC from jumping. Cc: Richard Cochran <richardcochran@gmail.com> Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com> Acked-by: Jacob Keller <jacob.e.keller@intel.com> Tested-by: Aaron Brown <aaron.f.brown@intel.com> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com> Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.