[PATCH v3 4/4] ARM: Implement PAN for LPAE by TTBR0 page table walks disablement

[Geert Uytterhoeven]

On Tue, May 14, 2024 at 8:26 PM Florian Fainelli <f.fainelli at gmail.com> wrote:
> On 5/14/24 10:03, Russell King (Oracle) wrote:
> > On Tue, May 14, 2024 at 09:54:07AM -0700, Florian Fainelli wrote:
> >> On 5/14/24 09:06, Geert Uytterhoeven wrote:
> >>> On Tue, May 14, 2024 at 1:28 PM Geert Uytterhoeven <geert at linux-m68k.org> wrote:
> >>> I ran tools/testing/ktest/config-bisect.pl and found the "offending"
> >>> config option: CONFIG_CC_OPTIMIZE_FOR_SIZE=y gives a broken
> >>> kernel, CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE=y works.
> >>> (verified by just enabling CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE in my
> >>>    broken config)....
> >>
> >> I second that, my working configuration has
> >> CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE=y whereas my
> >> broken one has CONFIG_CC_OPTIMIZE_FOR_SIZE=y, sure enough, changing the
> >> broken configuration to have CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE=y turns it
> >> into a "working" configuration on the Raspberry Pi 4B in AArch32 mode.
> >>
> >> That makes more sense because BCM7211 and BCM2711 are exactly the same CPU,
> >> thanks for restoring sanity!
> >
> > I would imagine that the problem is cpu_set_ttbcr(). Please try adding
> > a "memory" clobber to the asm() instruction in there.
> >
>
> I can confirm that with CONFIG_CC_OPTIMIZE_FOR_SIZE=y and the hunk below:
>
> diff --git a/arch/arm/include/asm/proc-fns.h
> b/arch/arm/include/asm/proc-fns.h
> index 9b3105a2a5e0..1087bd2af433 100644
> --- a/arch/arm/include/asm/proc-fns.h
> +++ b/arch/arm/include/asm/proc-fns.h
> @@ -187,7 +187,7 @@ static inline unsigned int cpu_get_ttbcr(void)
>
>   static inline void cpu_set_ttbcr(unsigned int ttbcr)
>   {
> -       asm("mcr p15, 0, %0, c2, c0, 2" : : "r" (ttbcr));
> +       asm("mcr p15, 0, %0, c2, c0, 2" : : "r" (ttbcr) : "memory");
>   }
>
>   #else  /*!CONFIG_MMU */
>
> my Raspberry Pi 4B in AArch32 mode boots and runs user-space properly.
>
> Thanks a lot Russell!

Unfortunately this does not fix the issue for me.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds