Messages in this thread | | | Date | Thu, 19 Oct 2023 14:48:29 +0200 | From | Andrea della Porta <> | Subject | Re: [PATCH 3/4] arm64/entry-common: Make Aarch32 syscalls' availability depend on aarch32_enabled() |
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On 13:57 Wed 18 Oct , Mark Rutland wrote: > On Wed, Oct 18, 2023 at 01:13:21PM +0200, Andrea della Porta wrote: > > Another major aspect of supporting running of 32bit processes is the > > ability to access 32bit syscalls. Such syscalls can be invoked by > > using the svc instruction. > > > > If Aarch32 emulation is disabled ensure that calling svc results > > in the same behavior as if CONFIG_COMPAT has not been enabled (i.e. > > a kernel panic). > > It's not "emulation" it's directly supported by the hardware.
You're right. I also struggled to use this label but I just reused the same name from Nikolai's patchset for x86, in the hope that the option would be more recognizable (something like 'ARCH_emulation' that could be used maybe for other platforms as well), but I agree with you that this is highly misleading. I will change it to something more straightforward.
> > > > > Signed-off-by: Andrea della Porta <andrea.porta@suse.com> > > --- > > arch/arm64/kernel/entry-common.c | 25 ++++++++++++++++++++++--- > > 1 file changed, 22 insertions(+), 3 deletions(-) > > > > diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c > > index 69ff9b8c0bde..32761760d9dd 100644 > > --- a/arch/arm64/kernel/entry-common.c > > +++ b/arch/arm64/kernel/entry-common.c > > @@ -802,6 +802,11 @@ asmlinkage void noinstr el0t_64_error_handler(struct pt_regs *regs) > > } > > > > #ifdef CONFIG_COMPAT > > +UNHANDLED(el0t, 32, sync_ni) > > +UNHANDLED(el0t, 32, irq_ni) > > +UNHANDLED(el0t, 32, fiq_ni) > > +UNHANDLED(el0t, 32, error_ni) > > IRQ, FIQ, and SError are not syscalls, so the commit title is bad.
Agreed. I'll call them exceptions.
> > > + > > static void noinstr el0_cp15(struct pt_regs *regs, unsigned long esr) > > { > > enter_from_user_mode(regs); > > @@ -821,6 +826,11 @@ static void noinstr el0_svc_compat(struct pt_regs *regs) > > > > asmlinkage void noinstr el0t_32_sync_handler(struct pt_regs *regs) > > { > > + if (!aarch32_enabled()) { > > + el0t_32_sync_ni_handler(regs); > > + return; > > + } > > Why do we have to do this at all? > > If we don't have AArch32 tasks, these paths are unreachable. Why do we need to > check that they aren't called? > > Mark.
Agreed. Please see also my previous comments here: https://lore.kernel.org/lkml/ZTEKabxNdegsbxyv@apocalypse/ https://lore.kernel.org/lkml/ZTD0DAes-J-YQ2eu@apocalypse/
but again, that's only speculative as of now, so we can ignore that part.
Andrea
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