On Fri, Dec 12, 2025 at 12:10:19PM +0100, Ahmad Fatoum wrote:
> Splitting mmu_disable into two noinline function on a RK3568 leads to a
> barebox crash, because the code has the implicit assumption that the
> compiler won't generate memory accesses including spilling to stack.
>
> We can't guarantee this in C code, so implement the procedure in
> assembly.
>
> While at it, drop mmu_early_disable(), which is unused, superfluous and
> suffers from the same issue as old mmu_disable().
>
> Signed-off-by: Ahmad Fatoum <[email protected]>
> ---
> v1 -> v2:
> - fix copy-paste problem in some ELs (Ulrich)
> ---
> arch/arm/cpu/cache-armv8.S | 54 ++++++++++++++++++++++++++++++++++++
> arch/arm/cpu/mmu_64.c | 27 +-----------------
> arch/arm/include/asm/cache.h | 1 +
> arch/arm/include/asm/mmu.h | 1 -
> 4 files changed, 56 insertions(+), 27 deletions(-)
>
> diff --git a/arch/arm/cpu/cache-armv8.S b/arch/arm/cpu/cache-armv8.S
> index 9d9e0fb585a1..130338d6034f 100644
> --- a/arch/arm/cpu/cache-armv8.S
> +++ b/arch/arm/cpu/cache-armv8.S
> @@ -9,6 +9,7 @@
>
> #include <linux/linkage.h>
> #include <init.h>
> +#include <asm/system.h>
>
> /*
> * void v8_flush_dcache_level(level)
> @@ -120,6 +121,59 @@ ENTRY(v8_invalidate_dcache_all)
> ret
> ENDPROC(v8_invalidate_dcache_all)
>
> +/*
> + * void v8_mmu_disable(void)
> + *
> + * Implements the equivalent of following C code:
> + *
> + * set_cr(get_cr() & ~(CR_M | CR_C))
> + * v8_flush_dcache_all();
> + * tlb_invalidate();
> + *
> + * dsb();
> + * isb();
> + *
> + * As D$ needs to be cleaned after it was disabled, this procedure
> + * is not permitted to trigger memory access, including spilling
> + * locals to stack. It's thus necessarily needs to be implemented
> + * in assembly.
> + */
> +.section .text.v8_mmu_disable
> +ENTRY(v8_mmu_disable)
> + mov x14, lr
> + mov x1, #~(CR_C | CR_M)
> + mrs x0, currentel
> + lsr w0, w0, #2 /* w0 <- current exception level */
> + cmp w0, #0x1
> + b.eq 1f
> + cmp w0, #0x2
> + b.eq 2f
The switch_el macro could be used here.
Sascha
> +3: /* EL3 */
> + mrs x0, sctlr_el3
> + and x0, x0, x1
> + msr sctlr_el3, x0
> + bl v8_flush_dcache_all
> + tlbi alle3
> + b 0f
> +2: /* EL2 */
> + mrs x0, sctlr_el2
> + and x0, x0, x1
> + msr sctlr_el2, x0
> + bl v8_flush_dcache_all
> + tlbi alle2
> + b 0f
> +1: /* EL1 */
> + mrs x0, sctlr_el1
> + and x0, x0, x1
> + msr sctlr_el1, x0
> + bl v8_flush_dcache_all
> + tlbi vmalle1
> +0: /* common prologue */
> + dsb sy
> + isb
> + ret x14
> +ENDPROC(v8_mmu_disable)
> +
> /*
> * void v8_flush_dcache_range(start, end)
> *
> diff --git a/arch/arm/cpu/mmu_64.c b/arch/arm/cpu/mmu_64.c
> index f22fcb5f8ea4..56c6a21f2b2a 100644
> --- a/arch/arm/cpu/mmu_64.c
> +++ b/arch/arm/cpu/mmu_64.c
> @@ -344,17 +344,7 @@ void __mmu_init(bool mmu_on)
>
> void mmu_disable(void)
> {
> - unsigned int cr;
> -
> - cr = get_cr();
> - cr &= ~(CR_M | CR_C);
> -
> - set_cr(cr);
> - v8_flush_dcache_all();
> - tlb_invalidate();
> -
> - dsb();
> - isb();
> + v8_mmu_disable();
> }
>
> void dma_inv_range(void *ptr, size_t size)
> @@ -436,18 +426,3 @@ void mmu_early_enable(unsigned long membase, unsigned
> long memsize, unsigned lon
>
> mmu_enable();
> }
> -
> -void mmu_early_disable(void)
> -{
> - unsigned int cr;
> -
> - cr = get_cr();
> - cr &= ~(CR_M | CR_C);
> -
> - set_cr(cr);
> - v8_flush_dcache_all();
> - tlb_invalidate();
> -
> - dsb();
> - isb();
> -}
> diff --git a/arch/arm/include/asm/cache.h b/arch/arm/include/asm/cache.h
> index dd022c1f23f2..ea78ae123aec 100644
> --- a/arch/arm/include/asm/cache.h
> +++ b/arch/arm/include/asm/cache.h
> @@ -15,6 +15,7 @@ void v8_flush_dcache_all(void);
> void v8_invalidate_dcache_all(void);
> void v8_flush_dcache_range(unsigned long start, unsigned long end);
> void v8_inv_dcache_range(unsigned long start, unsigned long end);
> +void v8_mmu_disable(void);
>
> static inline void icache_invalidate(void)
> {
> diff --git a/arch/arm/include/asm/mmu.h b/arch/arm/include/asm/mmu.h
> index eef6c53b5912..1fafbf9d77be 100644
> --- a/arch/arm/include/asm/mmu.h
> +++ b/arch/arm/include/asm/mmu.h
> @@ -65,6 +65,5 @@ void __dma_flush_range(unsigned long, unsigned long);
> void __dma_inv_range(unsigned long, unsigned long);
>
> void mmu_early_enable(unsigned long membase, unsigned long memsize, unsigned
> long barebox_base);
> -void mmu_early_disable(void);
>
> #endif /* __ASM_MMU_H */
> --
> 2.47.3
>
>
>
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