Deeply sorry, the cover-letter was forgotten to send to LKML. Here it is: On 2020/8/17 14:23, Lai Jiangshan wrote:
From: Lai Jiangshan <[email protected]> 7f2590a110b8("x86/entry/64: Use a per-CPU trampoline stack for IDT entries") has resulted that when exception on userspace, the kernel (error_entry) always push the pt_regs to entry stack(sp0), and then copy them to the kernel stack. And recent x86/entry work makes interrupt also use idtentry and makes all the interrupt code save the pt_regs on the sp0 stack and then copy it to the thread stack like exception. This is hot path (page fault, ipi), such overhead should be avoided. And the original interrupt_entry directly switches to kernel stack and pushes pt_regs to kernel stack. We should do it for error_entry. This is the job of patch1. Patch 2-3 simplify stack switching for .Lerror_bad_iret by just doing all the work in one function (fixup_bad_iret()). The patch set is based on v5.9-rc1 Changed from V1: based on tip/master -> based on tip/x86/entry patch 1 replaces the patch1,2 of V1, it borrows the original interrupt_entry's code into error_entry. patch2-4 is V1's patch3-5, unchanged (but rebased) Changed from V2: (re-)based on v5.9-rc1 drop the patch4 of V2 patchset Cc: Andy Lutomirski <[email protected]>, Cc: Thomas Gleixner <[email protected]>, Cc: Ingo Molnar <[email protected]>, Cc: Borislav Petkov <[email protected]>, Cc: [email protected], Cc: "H. Peter Anvin" <[email protected]>, Cc: Peter Zijlstra <[email protected]>, Cc: Alexandre Chartre <[email protected]>, Cc: "Eric W. Biederman" <[email protected]>, Cc: Jann Horn <[email protected]>, Cc: Dave Hansen <[email protected]> Lai Jiangshan (3): x86/entry: avoid calling into sync_regs() when entering from userspace x86/entry: directly switch to kernel stack when .Lerror_bad_iret x86/entry: remove unused sync_regs() arch/x86/entry/entry_64.S | 52 +++++++++++++++++++++++------------- arch/x86/include/asm/traps.h | 1 - arch/x86/kernel/traps.c | 22 +++------------ 3 files changed, 38 insertions(+), 37 deletions(-)
