linux-kernel - Re: [PATCH 1/2] x86: save r11 into pt

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Date:	Mon, 9 Mar 2015 17:02:32 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86: save r11 into pt_regs->flags on SYSCALL64
 fastpath


* Denys Vlasenko <dvlasenk@...hat.com> wrote:

> Before this patch, r11 was saved in pt_regs->r11.
> Which looks natural, but requires messy shuffling to/from iret frame
> whenever ptrace or e.g. iopl wants to modify flags - because
> that's how this register is used by SYSCALL/SYSRET.
> 
> This patch saves r11 in pt_regs->flags,
> and uses that value for SYSRET64 insn. Shuffling is eliminated.
> 
> stub_iopl is no longer needed: pt_regs->flags needs no fixing up.

Could you please split this into two patches: R11 saving, and 
stub_iopl removal?

For x86/asm changes we want as small changes as physically possible.

Thanks,

	Ingo
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