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

[Peter Maydell]

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.

-- PMM