Re: [Qemu-arm] [Qemu-devel] [PATCH] target/arm: Allow to switch from MON->HYP on AArch32

[Alexander Graf]

On 10.01.19 00:08, Peter Maydell wrote:
> On Wed, 9 Jan 2019 at 17:14, Alexander Graf <address@hidden> wrote:
>>
>> On 01/09/2019 05:59 PM, Peter Maydell wrote:
>>> On Wed, 9 Jan 2019 at 16:52, Peter Maydell <address@hidden> wrote:
>>>> On Wed, 9 Jan 2019 at 15:26, Alexander Graf <address@hidden> wrote:
>>>>> In U-boot, we switch from S-SVC -> MON -> HYP when we want to enter
>>>>> HYP mode. This dance seems to work ok (hence it's there in the code
>>>>> base), but breaks with current QEMU.
>>> PS: it would be helpful if the commit message said how u-boot
>>> is trying to go from Mon to Hyp -- some ways to try to do
>>> this are OK, and some are not, so whether it's supposed to
>>> work or not depends on what u-boot is actually doing...
>>
>> I don't fully understand all of it to be honest :). But the code is here:
>>
>> http://git.denx.de/?p=u-boot.git;a=blob;f=arch/arm/cpu/armv7/nonsec_virt.S
>>
>> What I managed to understand so far is that it goes to MON using the smc
>> #0 call and then changes SPSR so that on return (movs pc) the mode will
>> be different.
> 
> Thanks -- yes, that's an exception return so it's the
> expected way to go from Mon to Hyp.

That was my understanding, yes. Do you still want me to change the
commit message to mention that or will you just do it when applying?

Thanks,

Alex