From ae852495be365f6be433dde6629d3f0316f8efde Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Sun, 14 Oct 2018 11:38:18 -0700 Subject: [PATCH] x86/entry/64: Further improve paranoid_entry comments Commit: 16561f27f94e ("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 Acked-by: Thomas Gleixner Cc: Borislav Petkov Cc: Dave Hansen Cc: Linus Torvalds Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/c47daa1888dc2298e7e1d3f82bd76b776ea33393.1539542111.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/entry/entry_64.S | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 1d9b4a3..f95dcb2 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -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 -- 2.7.4