[PATCH v2] arm64: fix cleared E0POE bit after cpu_suspend()/resume()

[Yeoreum Yun]

TCR2_ELx.E0POE is set during smp_init().
However, this bit is not reprogrammed when the CPU enters suspension and
later resumes via cpu_resume(), as __cpu_setup() does not re-enable E0POE
and there is no save/restore logic for the TCR2_ELx system register.

As a result, the E0POE feature no longer works after cpu_resume().

To address this, save and restore TCR2_EL1 in the cpu_suspend()/cpu_resume()
path, rather than adding related logic to __cpu_setup(), taking into account
possible future extensions of the TCR2_ELx feature.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: bf83dae90fbc ("arm64: enable the Permission Overlay Extension for EL0")
Signed-off-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>
---

Patch History
==============
from v1 to v2:
  - following @Kevin Brodsky suggestion.
  - https://lore.kernel.org/all/20260105200707.2071169-1-yeoreum.yun@xxxxxxx/

NOTE:
  This patch based on v6.19-rc4
---
 arch/arm64/include/asm/suspend.h | 2 +-
 arch/arm64/mm/proc.S             | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/suspend.h b/arch/arm64/include/asm/suspend.h
index e65f33edf9d6..e9ce68d50ba4 100644
--- a/arch/arm64/include/asm/suspend.h
+++ b/arch/arm64/include/asm/suspend.h
@@ -2,7 +2,7 @@
 #ifndef __ASM_SUSPEND_H
 #define __ASM_SUSPEND_H

-#define NR_CTX_REGS 13
+#define NR_CTX_REGS 14
 #define NR_CALLEE_SAVED_REGS 12

 /*
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 01e868116448..5d907ce3b6d3 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -110,6 +110,10 @@ SYM_FUNC_START(cpu_do_suspend)
 	 * call stack.
 	 */
 	str	x18, [x0, #96]
+alternative_if ARM64_HAS_TCR2
+	mrs	x2, REG_TCR2_EL1
+	str	x2, [x0, #104]
+alternative_else_nop_endif
 	ret
 SYM_FUNC_END(cpu_do_suspend)

@@ -144,6 +148,10 @@ SYM_FUNC_START(cpu_do_resume)
 	msr	tcr_el1, x8
 	msr	vbar_el1, x9
 	msr	mdscr_el1, x10
+alternative_if ARM64_HAS_TCR2
+	ldr	x2, [x0, #104]
+	msr	REG_TCR2_EL1, x2
+alternative_else_nop_endif

 	msr	sctlr_el1, x12
 	set_this_cpu_offset x13
--
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}