Commit ae852495 authored Oct 14, 2018 by Andy Lutomirski Committed by Ingo Molnar Oct 17, 2018

x86/entry/64: Further improve paranoid_entry comments



Commit:

  16561f27 ("x86/entry: Add some paranoid entry/exit CR3 handling comments")

... added some comments.  This improves them a bit:

 - When I first read the new comments, it was unclear to me whether
   they were referring to the case where paranoid_entry interrupted
   other entry code or where paranoid_entry was itself interrupted.
   Clarify it.

 - Remove the EBX comment.  We no longer use EBX as a SWAPGS
   indicator.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/c47daa1888dc2298e7e1d3f82bd76b776ea33393.1539542111.git.luto@kernel.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 04f4f954

arch/x86/entry/entry_64.S

+4 −6

Original line number	Diff line number	Diff line
		@@ -1189,15 +1189,13 @@ ENTRY(paranoid_entry)
		1:
		/*
		* Always stash CR3 in %r14. This value will be restored,
		* verbatim, at exit. Needed if kernel is interrupted
		* after switching to the user CR3 value but before
		* returning to userspace.
		* verbatim, at exit. Needed if paranoid_entry interrupted
		* another entry that already switched to the user CR3 value
		* but has not yet returned to userspace.
		*
		* This is also why CS (stashed in the "iret frame" by the
		* hardware at entry) can not be used: this may be a return
		* to kernel code, but with a user CR3 value. The %ebx flag
		* for SWAPGS is also unusable for CR3 because there is a
		* window with a user GS and a kernel CR3.
		* to kernel code, but with a user CR3 value.
		*/
		SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14