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From: Nadav Amit <namit@vmware.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Dave Hansen <dave.hansen@intel.com>,
	Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during early_init
Date: Wed, 7 Nov 2018 19:13:03 +0000	[thread overview]
Message-ID: <9A69025F-5B49-4A26-AB95-F6D36908983B@vmware.com> (raw)
In-Reply-To: <20181105140925.GD22467@hirez.programming.kicks-ass.net>

From: Peter Zijlstra
Sent: November 5, 2018 at 2:09:25 PM GMT
> To: Nadav Amit <namit@vmware.com>
> Cc: Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org, x86@kernel.org, H. Peter Anvin <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>, Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>, Andy Lutomirski <luto@kernel.org>, Kees Cook <keescook@chromium.org>, Dave Hansen <dave.hansen@intel.com>, Masami Hiramatsu <mhiramat@kernel.org>
> Subject: Re: [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during early_init
> 
> 
> On Fri, Nov 02, 2018 at 04:29:41PM -0700, Nadav Amit wrote:
>> diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
>> index aac0c1f7e354..367c1d0c20a3 100644
>> --- a/arch/x86/kernel/jump_label.c
>> +++ b/arch/x86/kernel/jump_label.c
>> @@ -52,7 +52,13 @@ static void __ref __jump_label_transform(struct jump_entry *entry,
>> 	jmp.offset = jump_entry_target(entry) -
>> 		     (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
>> 
>> -	if (early_boot_irqs_disabled)
>> +	/*
>> +	 * As long as we are in early boot, we can use text_poke_early(), which
>> +	 * is more efficient: the memory was still not marked as read-only (it
>> +	 * is only marked after poking_init()). This also prevents us from using
>> +	 * text_poke() before poking_init() is called.
>> +	 */
>> +	if (!early_boot_done)
>> 		poker = text_poke_early;
>> 
>> 	if (type == JUMP_LABEL_JMP) {
> 
> It took me a while to untangle init/maze^H^Hin.c... but I think this
> is all we need:
> 
> diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
> index aac0c1f7e354..ed5fe274a7d8 100644
> --- a/arch/x86/kernel/jump_label.c
> +++ b/arch/x86/kernel/jump_label.c
> @@ -52,7 +52,12 @@ static void __ref __jump_label_transform(struct jump_entry *entry,
> 	jmp.offset = jump_entry_target(entry) -
> 		     (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
> 
> -	if (early_boot_irqs_disabled)
> +	/*
> +	 * As long as we're UP and not yet marked RO, we can use
> +	 * text_poke_early; SYSTEM_BOOTING guarantees both, as we switch to
> +	 * SYSTEM_SCHEDULING before going either.
> +	 */
> +	if (system_state == SYSTEM_BOOTING)
> 		poker = text_poke_early;
> 
> 	if (type == JUMP_LABEL_JMP) {

Thanks for this change, I will incorporate it.

I wanted to point a small difference from my version. Although this version
ensures we are UP and the kernel is still RW, preemption is possible with
this version. I presume that it should not affect jump-labels, since it
switches between JMP and multi-byte NOPs.

Thanks,
Nadav

  parent reply	other threads:[~2018-11-07 19:13 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-02 23:29 [PATCH v3 0/7] x86/alternatives: text_poke() fixes Nadav Amit
2018-11-02 23:29 ` [PATCH v3 1/7] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Nadav Amit
2018-11-03 10:11   ` Jiri Kosina
2018-11-04 20:58   ` Thomas Gleixner
2018-11-05 18:14     ` Nadav Amit
2018-11-02 23:29 ` [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during early_init Nadav Amit
2018-11-05 12:39   ` Peter Zijlstra
2018-11-05 13:33     ` Peter Zijlstra
2018-11-05 14:09   ` Peter Zijlstra
2018-11-05 17:22     ` Andy Lutomirski
2018-11-05 17:49       ` Nadav Amit
2018-11-05 19:03         ` Andy Lutomirski
2018-11-05 19:25           ` Nadav Amit
2018-11-05 20:05             ` Andy Lutomirski
2018-11-05 20:28               ` Thomas Gleixner
2018-11-05 21:31                 ` Nadav Amit
2018-11-07 19:13     ` Nadav Amit [this message]
2018-11-08 10:41       ` Peter Zijlstra
2018-11-02 23:29 ` [PATCH v3 3/7] x86/mm: temporary mm struct Nadav Amit
2018-11-02 23:29 ` [PATCH v3 4/7] fork: provide a function for copying init_mm Nadav Amit
2018-11-02 23:29 ` [PATCH v3 5/7] x86/alternatives: initializing temporary mm for patching Nadav Amit
2018-11-02 23:29 ` [PATCH v3 6/7] x86/alternatives: use temporary mm for text poking Nadav Amit
2018-11-05 13:19   ` Peter Zijlstra
2018-11-05 13:30   ` Peter Zijlstra
2018-11-05 18:04     ` Nadav Amit
2018-11-06  8:20       ` Peter Zijlstra
2018-11-06 13:11         ` Peter Zijlstra
2018-11-06 18:11           ` Nadav Amit
2018-11-06 19:08             ` Peter Zijlstra
2018-11-02 23:29 ` [PATCH v3 7/7] x86/alternatives: remove text_poke() return value Nadav Amit

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