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SubjectRe: [PATCH 2/3] arm: introduce IRQ stacks
On Wed, Oct 21, 2020 at 02:42:48PM +0200, Arnd Bergmann wrote:
> (also resending this reply from @kernel.org)
>
> On Fri, Oct 16, 2020 at 12:19 PM Arnd Bergmann <arnd@arndb.de> wrote:
> > On Thu, Oct 8, 2020 at 9:20 AM Maninder Singh <maninder1.s@samsung.com> wrote:
> > >
> > > This patch adds code for switching to IRQ stack.
> > > IRQ stack and Kernel SVC stack have below design.
> > >
> > > IRQ STACK:-
> > > ------------ IRQ stack top
> > > | |
> > > ------------
> > > . .
> > > . .
> > > . .
> > > ------------
> > > | sp | <- irq_stack_base + 0x8
> > > ------------
> > > | fp | <- irq_stack_base + 0x4
> > > ------------
> > > |tinfo_ptr | /* pointer to thread info */
> > > irq_stack_ptr --> ------------ IRQ stack base
> > >
> > > Kernel SVC stack:-
> > > ------------ Kernel stack top
> > > | |
> > > ------------
> > > . .
> > > . .
> > > . .
> > > ------------
> > > | |
> > > | |
> > > ------------
> > > |tinfo_ptr | /* pointer to thread info */
> > > ------------ Kernel stack base
> >
> > The extra indirection doesn't look great, and I don't see any of the
> > other architectures need that. Since we can access percpu data
> > without going through thread_info, maybe doing the same as
> > x86 would work here:
> >
> > - define 'current' as 'this_cpu_read_stable(current_task);'
> > - convert to CONFIG_THREAD_INFO_IN_TASK

That means we need to also code that up in assembly - remember, we
need to access thread_info from assembly code.

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