linux-kernel - Re: [PATCH v2 0/6] x86: Rewrite switch

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Message-ID: <CAMzpN2ia05id1OxHbF-7VuQ7O-D4SV3THkq8btePfgeKbNDy9w@mail.gmail.com>
Date:	Sun, 19 Jun 2016 18:05:54 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 0/6] x86: Rewrite switch_to()

On Sat, Jun 18, 2016 at 4:56 PM, Brian Gerst <brgerst@...il.com> wrote:
> This patch set simplifies the switch_to() code, by moving the stack switch
> code out of line into an asm stub before calling __switch_to().  This ends
> up being more readable, and using the C calling convention instead of
> clobbering all registers improves code generation.  It also allows newly
> forked processes to construct a special stack frame to seamlessly flow
> to ret_from_fork, instead of using a test and branch, or an unbalanced
> call/ret.
>
> Changes from v1:
> - Added struct inactive_task_frame
> - Added comments about kernel threads returning to userspace
> - Cleaned up some incorrect uses of thread.sp

I forgot to also add:
- Rearranged inactive stack frame so that BP (frame pointer) is in the
natural position right below the return address.  This should take
care of unwinding issues Josh raised.

--
Brian Gerst