[PATCH] ARM64: setupc: drop erroneous cache flush of virt addr 0

[PATCH] ARM64: setupc: drop erroneous cache flush of virt addr 0

[Ahmad Fatoum]

From: Chali Anis <chalianis1@gmail.com>

relocate_to_adr copies around executable code and thus needs to
ensure coherence between I$ and D$. When the function was first added,
it didn't maintain cache correctly, because while it did call
arm_early_mmu_cache_flush(), back then that function did not invalidate
I$ after the D$ clean.

This likely went unnoticed, because a comment in relocate_to_adr
suggested that ic ivau is invalidating the I$, but in reality that
instruction did an unconditional invalidation of the single
cache line corresponding to virtual address 0 if it exists.

Back in 2019, sync_caches_for_execution() was introduced, which
correctly invalidates I$ after D$ cleaning, but the invalidation of
address 0 still remained.

On a 64-bit Tegra SoC with barebox running as EFI payload, it was
observed that this instruction was triggering a translation fault[1] at
address 0. The reason behind that is not completely understood, but it's
fixed by removing these two lines that are erroneous anyway, so let's do
that.

[1]: https://esr.arm64.dev/#0x96000147

Fixes: 868df08038a9 ("ARM: aarch64: Add relocation support")
Signed-off-by: Chali Anis <chalianis1@gmail.com>
Signed-off-by: Ahmad Fatoum <a.fatoum@barebox.org>
---
 arch/arm/cpu/setupc_64.S | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/arm/cpu/setupc_64.S b/arch/arm/cpu/setupc_64.S
index 2138c2a600fa..fd95187a0422 100644
--- a/arch/arm/cpu/setupc_64.S
+++ b/arch/arm/cpu/setupc_64.S
@@ -63,9 +63,6 @@ ENTRY(relocate_to_adr)
 
 	bl	sync_caches_for_execution
 
-	mov	x0,#0
-	ic	ivau, x0	/* flush icache */
-
 	adr_l	x0, 1f
 	sub	x0, x0, x20
 	add	x0, x0, x21
-- 
2.47.3

Re: [PATCH] ARM64: setupc: drop erroneous cache flush of virt addr 0

[Sascha Hauer]

On Fri, 12 Sep 2025 08:51:04 +0200, Ahmad Fatoum wrote:
> relocate_to_adr copies around executable code and thus needs to
> ensure coherence between I$ and D$. When the function was first added,
> it didn't maintain cache correctly, because while it did call
> arm_early_mmu_cache_flush(), back then that function did not invalidate
> I$ after the D$ clean.
> 
> This likely went unnoticed, because a comment in relocate_to_adr
> suggested that ic ivau is invalidating the I$, but in reality that
> instruction did an unconditional invalidation of the single
> cache line corresponding to virtual address 0 if it exists.
> 
> [...]

Applied, thanks!

[1/1] ARM64: setupc: drop erroneous cache flush of virt addr 0
      https://git.pengutronix.de/cgit/barebox/commit/?id=cca8ff2e8810 (link may not be stable)

Best regards,
-- 
Sascha Hauer <s.hauer@pengutronix.de>