Re: [PATCH v5 06/30] arm64: context switch POR_EL0 register

[Catalin Marinas <catalin.marinas@arm.com>]

On Fri, Aug 23, 2024 at 03:45:32PM +0100, Will Deacon wrote:
> On Thu, Aug 22, 2024 at 04:10:49PM +0100, Joey Gouly wrote:
> > +static void permission_overlay_switch(struct task_struct *next)
> > +{
> > +	if (!system_supports_poe())
> > +		return;
> > +
> > +	current->thread.por_el0 = read_sysreg_s(SYS_POR_EL0);
> > +	if (current->thread.por_el0 != next->thread.por_el0) {
> > +		write_sysreg_s(next->thread.por_el0, SYS_POR_EL0);
> > +		/* ISB required for kernel uaccess routines when chaning POR_EL0 */
> 
> nit: typo "chaning".
> 
> But more substantially, is this just to prevent spurious faults in the
> context of a new thread using a stale value for POR_EL0?

Not just prevent faults but enforce the permissions from the new
thread's POR_EL0. The kernel may continue with a uaccess routine from
here, we can't tell.

-- 
Catalin