Subject: [PATCH 1/2] arm: KVM: Do not update PC if the trap handler has updated it

From: [email-masked] (Marc Zyngier)
Date: Thu, 07 Jan 2016 09:05:06 +0000

On 07/01/16 08:59, Shannon Zhao wrote:
> 
> 
> On 2016/1/7 16:50, Marc Zyngier wrote:
>> On 22/12/15 14:50, Peter Maydell wrote:
>>> On 22 December 2015 at 14:39, Christoffer Dall
>>> <[email-masked]> wrote:
>>>> On Tue, Dec 22, 2015 at 11:08:10AM +0000, Peter Maydell wrote:
>>>>> Won't this result in our incorrectly skipping the first insn
>>>>> in the fault handler if the original offending instruction
>>>>> was itself the first insn in the fault handler?
>>>>>
>>>> Wouldn't that then loop with the exception forever?
>>>
>>> Yes, but so would real hardware...
>>
>> Indeed. As it is, this patch is not doing what it should. On the other
>> hand, I came to the conclusion that we do not need to fix this just yet,
>> as long as we only let KVM inject an UNDEF, and that's what the PMU code
>> requires.
>>
>> I'll comment on the PMU thread, but the gist of it is:
>> 1) fix the arm64 UNDEF/PABRT/DABRT code to properly account for the the
>> source EL (Table D1-7 of the ARMv8 ARM).
> This looks like something we add in the PMU patch set.
> 
> +		switch (cpsr & (PSR_MODE_MASK | PSR_MODE32_BIT)) {
> +		case PSR_MODE_EL0t:
> +			exc_offset = EL0_EXCEPT_SYNC_OFFSET_64;
> +			break;
> +		case PSR_MODE_EL1t:
> +			exc_offset = EL1_EXCEPT_BAD_SYNC_OFFSET;
> +			break;
> +		case PSR_MODE_EL1h:
> +			exc_offset = EL1_EXCEPT_SYNC_OFFSET;
> +			break;
> +		default:
> +			exc_offset = EL0_EXCEPT_SYNC_OFFSET_32;
> +		}
> +

Indeed, plus some additional code to select the actual vector and not be
limited to a Synchronous exception (even if that's the only thing we use
today).

See the patch I've just posted for more details.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...