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

[Peter Maydell <peter.maydell@linaro.org>]

On Thu, 10 Jan 2019 at 06:43, Alexander Graf <agraf@suse.de> wrote:
>
>
>
> On 10.01.19 00:08, Peter Maydell wrote:
> > On Wed, 9 Jan 2019 at 17:14, Alexander Graf <agraf@suse.de> wrote:
> >>
> >> On 01/09/2019 05:59 PM, Peter Maydell wrote:
> >>> On Wed, 9 Jan 2019 at 16:52, Peter Maydell <peter.maydell@linaro.org> wrote:
> >>>> On Wed, 9 Jan 2019 at 15:26, Alexander Graf <agraf@suse.de> 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?

I'll add a note when I apply it; thanks.

-- PMM