linux-kernel - Re: [PATCH 1/2] x86/asm/entry/64: Enable interrupts *after* we fetch PER_CPU_VAR(old

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Date:	Tue, 17 Mar 2015 11:04:39 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	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 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] x86/asm/entry/64: Enable interrupts *after* we fetch PER_CPU_VAR(old_rsp)

On Tue, Mar 17, 2015 at 6:42 AM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
> Without this change, it is still not possible to get rid of
> PER_CPU_VAR(old_rsp) usage in switch_to: if preemption happens
> while we did not fetch PER_CPU_VAR(old_rsp) and stored it in pt_regs->sp,
> PER_CPU_VAR(old_rsp) gets corrupted by other task's user sp.
>

[...]

> -       ENABLE_INTERRUPTS(CLBR_NONE)

[...]

> +       ENABLE_INTERRUPTS(CLBR_RAX)

In future patches, please don't sneak these things in.  It makes it
much harder to review.  If you need to move code and change it like
this, I think it should be clearly and explicitly mentioned in the
changelog.

--Andy
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