On Thu, Mar 22, 2018 at 06:29:59PM +0100, Peter Zijlstra wrote: > On Thu, Mar 22, 2018 at 10:00:37AM +0100, Dominik Brodowski wrote: > > Using the sched-internal do_sched_yield() helper allows us to get rid of > > the sched-internal call to the sys_sched_yield() syscall. > > > > This patch is part of a series which tries to remove in-kernel calls to > > syscalls. On this basis, the syscall entry path can be streamlined. > > But why !? Either Cc me on more of the series such that the whole makes > sense, or better yet, write a proper Changelog. Well, the summary is right there in the changelog: Kernel code simply should not pretend to be userspace and call a syscall function. For a more detailled description, see, for instance, Linus' explanation in http://lkml.kernel.org/r/CA+55aFwo7yA1gm8AUYMEQA8ZNY-9GGF8Oup09jJFvEa4J7C+jA@xxxxxxxxxxxxxx : | On x86-64, we'd like to just pass the 'struct pt_regs *' pointer, and | have the sys_xyz() function itself just pick out the arguments it | needs from there. | | That has a few reasons for it: | | - we can clear all registers at system call entry, which helps defeat | some of the "pass seldom used register with user-controlled value that | survives deep into the callchain" things that people used to leak | information | | - we can streamline the low-level system call code, which needs to | pass around 'struct pt_regs *' anyway, and the system call only picks | up the values it actually needs I can add such a long description to all these patches, but that seems to be a bit... longwinded. Thanks, Dominik
