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Date:   Mon, 7 Nov 2022 16:12:20 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     kernel test robot <oliver.sang@intel.com>
Cc:     oe-lkp@lists.linux.dev, lkp@intel.com,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        Dave Hansen <dave.hansen@intel.com>
Subject: Re: [tip:x86/mm] [x86/mm]  b389949485:
 WARNING:at_arch/x86/mm/pat/set_memory.c:#__change_page_attr
Message-ID: <Y2kgVE+etZ1+F2PW@hirez.programming.kicks-ass.net>
References: <202211061748.eb591682-oliver.sang@intel.com>
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In-Reply-To: <202211061748.eb591682-oliver.sang@intel.com>
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On Sun, Nov 06, 2022 at 08:38:27PM +0800, kernel test robot wrote:
> 
> Greeting,
> 
> FYI, we noticed WARNING:at_arch/x86/mm/pat/set_memory.c:#__change_page_attr due to commit (built with gcc-11):
> 
> commit: b38994948567e6d6b62947401c57f4ab2efe070c ("x86/mm: Implement native set_memory_rox()")
> https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git x86/mm
> 
> [test failed on linux-next/master 0cdb3579f1ee4c1e55acf8dfb0697b660067b1f8]
> 
> in testcase: boot
> 
> on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
> 
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
> 
> 
> If you fix the issue, kindly add following tag
> | Reported-by: kernel test robot <oliver.sang@intel.com>
> | Link: https://lore.kernel.org/oe-lkp/202211061748.eb591682-oliver.sang@intel.com
> 
> 
> [   44.943065][   T11] ------------[ cut here ]------------
> [   44.943725][   T11] CPA detected W^X violation: 0000000000000060 -> 0000000000000063 range: 0xffff8881beca5000 - 0xffff8881beca5fff PFN 1beca5
> [ 44.944929][ T11] WARNING: CPU: 0 PID: 11 at arch/x86/mm/pat/set_memory.c:609 __change_page_attr (arch/x86/mm/pat/set_memory.c:609 arch/x86/mm/pat/set_memory.c:1582) 
> [   44.945824][   T11] Modules linked in:
> [   44.946229][   T11] CPU: 0 PID: 11 Comm: kworker/0:1 Tainted: G        W          6.1.0-rc3-00010-gb38994948567 #1 f37474c2082f37dd433f70907b94c2b0df8d70b8
> [   44.947518][   T11] Workqueue: events bpf_prog_free_deferred
> [ 44.948074][ T11] RIP: 0010:__change_page_attr (arch/x86/mm/pat/set_memory.c:609 arch/x86/mm/pat/set_memory.c:1582) 

Urgh, as spotted by dhansen, the code in change_page_attr_set_clr(),
specifically the checkalias thing, seems to rely on single bit flips for
NX.

Let me try to make sense of this stuff....