Re: [RFC][PATCH] x86/mm: Sync all vmalloc mappings before text_poke()

From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Joerg Roedel <jroedel@suse.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Shile Zhang <shile.zhang@linux.alibaba.com>,
	Andy Lutomirski <luto@amacapital.net>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Tzvetomir Stoyanov <tz.stoyanov@gmail.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [RFC][PATCH] x86/mm: Sync all vmalloc mappings before text_poke()
Date: Wed, 29 Apr 2020 17:44:23 +0200	[thread overview]
Message-ID: <20200429154423.GM13592@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200429103216.34b6f7aa@gandalf.local.home>

On Wed, Apr 29, 2020 at 10:32:16AM -0400, Steven Rostedt wrote:
> On Wed, 29 Apr 2020 16:10:04 +0200
> Joerg Roedel <jroedel@suse.de> wrote:
> 
> > On Wed, Apr 29, 2020 at 10:07:31AM -0400, Steven Rostedt wrote:
> > > Talking with Mathieu about this on IRC, he pointed out that my code does
> > > have a vzalloc() that is called:
> > > 
> > > in trace_pid_write()
> > > 
> > > 	pid_list->pids = vzalloc((pid_list->pid_max + 7) >> 3);
> > > 
> > > This is done when -P1,2 is on the trace-cmd command line.  
> > 
> > Yeah, I was guessing something like this, init_mm has a mapping which
> > poking_mm has not. I currently try to reproduce this on one of my
> > machines.
> 
> Note, in use_temporary_mm(poking_mm), poking_mm only contains the page that

poking_mm should contain the full kernel map, the userspace part is 2
pages in a random location to alias two kernel pages.

So a vmalloc fault _should_ work.

> needs to be updated. But will get added to per_cpu(cpu_tlbstate.loaded_mm),
> which appears to be the one that's not updated.
> 
> -- Steve