Messages in this thread | | | Date | Wed, 6 Apr 2022 21:00:38 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH V4 1/7] x86/traps: Move pt_regs only in fixup_bad_iret() |
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On Fri, Mar 18, 2022 at 10:30:10PM +0800, Lai Jiangshan wrote: > From: Lai Jiangshan <jiangshan.ljs@antgroup.com> > > fixup_bad_iret() and sync_regs() have similar arguments and do similar > work that copies full or partial pt_regs to a place and switches stack > after return. They are quite the same, but fixup_bad_iret() not only > copies the pt_regs but also the return address of error_entry() while
What return address of error_entry()? You lost me here.
fixup_bad_iret() moves the stack frame while sync_regs() switches to the thread stack. I have no clue what you mean.
> sync_regs() copies the pt_regs only and the return address of > error_entry() was preserved and handled in ASM code.
Nope, no idea.
> This patch makes fixup_bad_iret() work like sync_regs() and the
Avoid having "This patch" or "This commit" in the commit message. It is tautologically useless.
Also, do
$ git grep 'This patch' Documentation/process
for more details.
> handling of the return address of error_entry() is moved in ASM code. > > It removes the need to use the struct bad_iret_stack, simplifies > fixup_bad_iret() and makes the ASM error_entry() call fixup_bad_iret() > as the same as calling sync_regs() which adds readability because > the calling patterns are exactly the same.
So fixup_bad_iret() gets the stack ptr passed in by doing:
mov %rsp, %rdi call fixup_bad_iret mov %rax, %rsp
and error_regs()
movq %rsp, %rdi /* arg0 = pt_regs pointer */ call sync_regs movq %rax, %rsp /* switch stack */
the same way.
Confused.
> It is prepared for later patch to do the stack switch after the > error_entry() which simplifies the code further.
Looking at your next patch, is all this dance done just so that you can do
leaq 8(%rsp), %rdi
in order to pass in pt_regs to both functions?
And get rid of the saving/restoring %r12?
Is that what the whole noise is about?
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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