linux-kernel - Re: RFC: (almost) getting rid of FIXUP/RESTORE_TOP_OF

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Message-ID: <54EC643D.3040005@redhat.com>
Date:	Tue, 24 Feb 2015 12:45:01 +0100
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
	X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alexander van Heukelum <heukelum@...tmail.fm>
Subject: Re: RFC: (almost) getting rid of FIXUP/RESTORE_TOP_OF_STACK?

On 02/24/2015 12:58 AM, Andy Lutomirski wrote:
>> - Next possible change is to use PUSH insns to build the stack. Something along the lines of
>>         swapgs
>>         mov     %rsp,%gs:old_rsp
>>         mov     %gs:kernel_stack,%rsp
>>         sti
>>         push    $__USER_DS   /* pt_regs->ss */
>>         push    %gs:old_rsp  /* ->rsp */
>>         push    %r11         /* ->rflags */
>>         push    $__USER_CS   /* ->cs */
>>         push    %rcx         /* ->rip */
>>         push    %rax         /* ->orig_rax */
>>         push    %rdi
>>         push    %rsi
>>         push    %rdx
>>         push    %rcx
>>         push    $-ENOSYS     /* ->rax */
>>         push    %r8
>>         push    %r9
>>         push    %r10
>>         push    %r11
>>         sub     $(6*8),%rsp /* rbx, rbp, r12-r15 not saved */

Correction:
         push    %r11
         sub     $(6*8),%rsp /* rbx, rbp, r12-r15 not saved */
should be
         sub     $(7*8),%rsp /* r11, rbx, rbp, r12-r15 not saved */
since we don't need to save r11 either.

> 
> Yay!

"yay!" as in "I like this!" or as in "I am surprised" ?

>  Can we have a macro PUSH_XYZ for most of this?

Yes, it can be a macro. I'm not sure we'll have more than one
such place, tho.
Do you want a macro even if it will be once-use only?

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