linux-kernel - Re: [PATCH] pci: imx6: support kernels built in Thumb-2 mode

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Date:   Wed, 28 Nov 2018 19:52:44 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Trent Piepho <tpiepho@...inj.com>,
        "stefan@...er.ch" <stefan@...er.ch>,
        "hongxing.zhu@....com" <hongxing.zhu@....com>,
        "l.stach@...gutronix.de" <l.stach@...gutronix.de>
Cc:     "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "andrew.smirnov@...il.com" <andrew.smirnov@...il.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "leonard.crestez@....com" <leonard.crestez@....com>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] pci: imx6: support kernels built in Thumb-2 mode

On 28/11/2018 18:56, Trent Piepho wrote:
> On Wed, 2018-11-28 at 16:16 +0000, Robin Murphy wrote:
>>
>>>    
>>> +static int imx6q_pcie_abort_handler_thumb2(unsigned long addr,
>>> +		unsigned int fsr, struct pt_regs *regs)
>>> +{
>>> +	unsigned long pc = instruction_pointer(regs);
>>> +	unsigned long instr = *(unsigned long *)pc;
>>> +	unsigned long thumb2_instr = __mem_to_opcode_thumb16(instr);
>>> +	int reg = thumb2_instr & 7;
>>> +
>>> +	if (!__opcode_is_thumb16(instr & 0x0000ffffUL))
>>> +		return 1;
>>
>> There are plenty of 32-bit Thumb encodings of various LDR/STR variants,
>> and I doubt we can guarantee that the offset, target register, and/or
>> addressing mode for a config space access will *always* suit the
>> (relatively limited) 16-bit ones.
> 
> It might be the case that PLD/PLI, 32-bit thumb2 instructions, could
> trigger an abort too.

Preload instructions shouldn't cause a *synchronous* abort, which is 
what we're trapping here, and they could only result in an asynchronous 
abort coming back later if the address is mapped as Normal memory, which 
it really shouldn't be in this case. Frankly either way, anyone even 
thinking about trying to pull PCI config space into data caches, let 
alone instruction caches, probably deserves everything they get ;)

Robin.