Re: [PATCH v3 04/10] ARM: add file for HYP mode related setup

From: Sascha Hauer <s.hauer@pengutronix.de>
To: Lucas Stach <l.stach@pengutronix.de>
Cc: barebox@lists.infradead.org
Subject: Re: [PATCH v3 04/10] ARM: add file for HYP mode related setup
Date: Wed, 11 Apr 2018 10:41:20 +0200	[thread overview]
Message-ID: <20180411084120.cxoyjrvp7f52aus2@pengutronix.de> (raw)
In-Reply-To: <1523357612.4981.5.camel@pengutronix.de>

On Tue, Apr 10, 2018 at 12:53:32PM +0200, Lucas Stach wrote:
> Am Donnerstag, den 05.04.2018, 09:54 +0200 schrieb Sascha Hauer:
> > On Mon, Mar 26, 2018 at 09:20:19PM +0200, Lucas Stach wrote:
> > > This adds routines to add hyp mode vectors and switch back to HYP
> > > mode from SVC. This is needed in both the PBL and Barebox proper.
> > > 
> > > > > Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> > > > > Tested-by: Roland Hieber <r.hieber@pengutronix.de>
> > > ---
> > > v3:
> > > - fix whitespace
> > > - use __BARE_INIT
> > > ---
> > >  arch/arm/cpu/Makefile         |   4 ++
> > >  arch/arm/cpu/hyp.S            | 116 ++++++++++++++++++++++++++++++++++++++++++
> > >  arch/arm/cpu/sm_as.S          |  11 ----
> > >  arch/arm/include/asm/secure.h |   8 +++
> > >  4 files changed, 128 insertions(+), 11 deletions(-)
> > >  create mode 100644 arch/arm/cpu/hyp.S
> > > 
> > > diff --git a/arch/arm/cpu/Makefile b/arch/arm/cpu/Makefile
> > > index 13fe12c31f6f..f86dff975bb4 100644
> > > --- a/arch/arm/cpu/Makefile
> > > +++ b/arch/arm/cpu/Makefile
> > > @@ -9,6 +9,10 @@ obj-$(CONFIG_ARM_EXCEPTIONS) += exceptions.o
> > >  obj-$(CONFIG_MMU) += mmu.o mmu-early.o
> > >  pbl-$(CONFIG_MMU) += mmu-early.o
> > >  lwl-y += lowlevel.o
> > > +obj-y += hyp.o
> > > +AFLAGS_hyp.o :=-Wa,-march=armv7-a -Wa,-mcpu=all
> > > +pbl-y += hyp.o
> > > +AFLAGS_pbl-hyp.o :=-Wa,-march=armv7-a -Wa,-mcpu=all
> > >  endif
> > >  
> > >  obj-$(CONFIG_ARM_EXCEPTIONS) += interrupts.o
> > > diff --git a/arch/arm/cpu/hyp.S b/arch/arm/cpu/hyp.S
> > > new file mode 100644
> > > index 000000000000..1314b56eab25
> > > --- /dev/null
> > > +++ b/arch/arm/cpu/hyp.S
> > > @@ -0,0 +1,116 @@
> > > +#include <linux/linkage.h>
> > > +#include <asm/system.h>
> > > +#include <asm/opcodes-virt.h>
> > > +#include <init.h>
> > > +
> > > +.arch_extension sec
> > > +.arch_extension virt
> > > +
> > > +__BARE_INIT
> > > +
> > > +.data
> > > > > +	.align  2
> > > +ENTRY(__boot_cpu_mode)
> > > > > +	.long   0
> > > +.text
> > > +
> > > +ENTRY(__hyp_install)
> > > > > > > +	mrs	r12, cpsr
> > > > > > > +	and	r12, r12, #MODE_MASK
> > > +
> > > > > +	@ Save the initial CPU state
> > > > > > > +	adr	r0, .L__boot_cpu_mode_offset
> > > > > > > +	ldr	r1, [r0]
> > > +	str	r12, [r0, r1]
> > 
> > Naa, this won't work. You save the cpsr value in __boot_cpu_mode, but
> > this variable exists both in PBL and regular barebox, __hyp_install
> > is called multiple times and cpsr is modified right after saving it.
> 
> It does. ;)
> 
> I guess its non-obvious from the code flow, but what we do is to drop
> down to SVC in the PBL, then jump back to HYP before starting barebox
> proper and the dropping down to SVC again on barebox entry.
> All in all this is less-than-pretty, but IMHO it's the lesser evil than
> trying to implement some communication channel from PBL to barebox
> proper to pass information like this.
> 
> So I guess this code needs some more comments...

Yep ;)

Sascha

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