On 16 December 2024 23:24:07 GMT, David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote: >Fix a few bugs introduced by the recent rework of the relocate_kernel() >code, and one which has been there in the kjump code from the beginning. > > • Global read-only TLB entries made relocate_kernel() crash when writing > to its own page after the %cr3 switch should have made it writeable. > • The preserve_context flag was lost when invoking swap_pages on the way > back, causing pages not to be swapped. > • The wrong page was being used as the swap page. > • The ABI for the kjump call asks the callee to put its entry address for > next time at %rsp+8 before returning, but we set %rsp to the top of the > available page, such that the entry address is at the start of some > other page. > • The relocate_kernel() function lacked Clang CFI information, but is now > called via a function pointer, leading to a crash¹. > • The relocate_kernel() code and data could end up being linked into the > wrong place for a LTO / -ffunction-sections build. > >Thanks to Nathan for reporting many of the above. > >Also a few minor cleanups, including a comments-only patch from Rafael >on the suspend-like part of kjump as a prelude to actually cleaning that >up. > >¹ Fixed by just adding __nocfi. Actually providing the CFI information >for relocate_kernel() will need a bit more work, so let's just do the >simple fix for now. > >David Woodhouse (7): > x86/kexec: Disable global pages before writing to control page > x86/kexec: Ensure preserve_context flag is set on return to kernel > x86/kexec: Use correct swap page in swap_pages function > x86/kexec: Fix stack and handling of re-entry point for ::preserve_context > x86/kexec: Mark machine_kexec() with __nocfi > x86/kexec: Cope with relocate_kernel() not being at the start of the page > x86/kexec: Use typedef for relocate_kernel_fn function prototype > >Nathan Chancellor (1): > x86/kexec: Fix location of relocate_kernel with -ffunction-sections > >Rafael J. Wysocki (1): > kexec_core: Add and update comments regarding the KEXEC_JUMP flow > > arch/x86/include/asm/kexec.h | 26 ++++++++-------- > arch/x86/kernel/machine_kexec_32.c | 7 +---- > arch/x86/kernel/machine_kexec_64.c | 8 ++--- > arch/x86/kernel/relocate_kernel_64.S | 57 ++++++++++++++++++++++++------------ > arch/x86/kernel/vmlinux.lds.S | 4 +-- > kernel/kexec_core.c | 23 +++++++++++---- > 6 files changed, 74 insertions(+), 51 deletions(-) > > Ping? I made sure I got this series out quickly as it deals with regressions in tip/x86/boot. Aside from potentially being able to save a byte on one instruction, I think the rest of the discussion has been resolved without changing the patches. I'll resend the follow-on parts which add the debugging support when I'm back at a real keyboard.
