Re: [PATCH v3 7/9] KVM: arm/arm64: Only clean the dcache on translation fault

Marc Zyngier
2018-08-21T13:57:35Z

On 21/08/18 14:35, Alexander Graf wrote:
> On 10/23/2017 06:11 PM, Marc Zyngier wrote:
>> The only case where we actually need to perform a dcache maintenance
>> is when we map the page for the first time, and subsequent permission
>> faults do not require cache maintenance. Let's make it conditional
>> on not being a permission fault (and thus a translation fault).
>>
>> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>
> This patch unfortunately breaks something on Hi1616 SoCs when running
> 32bit guests. With this patch applied (and thus with 4.18) I get random
> illegal instruction warnings from 32bit code inside VMs. I do not know
> at this point whether this affects other CPUs as well.

Can you please give a few more details?

- what are the CPUs on this Hi1616? At least a /proc/cpuinfo would help

- an example of the crash? Is it within the decompressor? After? This
things do matter, given the number of crazy things the 32bit kernel does

- a host kernel configuration?

> If anyone is interested in a reproducer, I have something handy. But for
> now I believe we should just revert this patch.

Before we revert anything, I'd like to understand what is happening.

Thanks,

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