On Tue, Feb 27, 2018 at 02:18:36PM -0500, Waiman Long wrote: > > + /* Make sure we are running on kernel cr3 */ > > + SWITCH_TO_KERNEL_CR3 scratch_reg=%eax > > + > > xorl %edx, %edx # error code 0 > > movl %esp, %eax # pt_regs pointer > > > > The debug exception calls ret_from_exception on exit. If coming from > userspace, the C function prepare_exit_to_usermode() will be called. > With the PTI-32 code, it means that function will be called with the > entry stack instead of the task stack. This can be problematic as macro > like current won't work anymore. Okay, I had another look at the debug handler. As I said before, it already handles the from-entry-stack case, but with these patches it gets more likely that we actually hit that path. Also, with the special handling for from-kernel-with-entry-stack situations we can simplify the debug handler and make it more robust with the diff below. Thoughts? diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 8c149f5..844aff1 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -1318,33 +1318,14 @@ ENTRY(debug) ASM_CLAC pushl $-1 # mark this as an int - SAVE_ALL + SAVE_ALL switch_stacks=1 ENCODE_FRAME_POINTER - /* Make sure we are running on kernel cr3 */ - SWITCH_TO_KERNEL_CR3 scratch_reg=%eax - xorl %edx, %edx # error code 0 movl %esp, %eax # pt_regs pointer - /* Are we currently on the SYSENTER stack? */ - movl PER_CPU_VAR(cpu_entry_area), %ecx - addl $CPU_ENTRY_AREA_entry_stack + SIZEOF_entry_stack, %ecx - subl %eax, %ecx /* ecx = (end of entry_stack) - esp */ - cmpl $SIZEOF_entry_stack, %ecx - jb .Ldebug_from_sysenter_stack - - TRACE_IRQS_OFF - call do_debug - jmp ret_from_exception - -.Ldebug_from_sysenter_stack: - /* We're on the SYSENTER stack. Switch off. */ - movl %esp, %ebx - movl PER_CPU_VAR(cpu_current_top_of_stack), %esp TRACE_IRQS_OFF call do_debug - movl %ebx, %esp jmp ret_from_exception END(debug) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
