arm64: vmlinux.ld: Add mmuoff data sections and move mmuoff text into idmap

Resume from hibernate needs to clean any text executed by the kernel with
the MMU off to the PoC. Collect these functions together into the
.idmap.text section as all this code is tightly coupled and also needs
the same cleaning after resume.

Data is more complicated, secondary_holding_pen_release is written with
the MMU on, clean and invalidated, then read with the MMU off. In contrast
__boot_cpu_mode is written with the MMU off, the corresponding cache line
is invalidated, so when we read it with the MMU on we don't get stale data.
These cache maintenance operations conflict with each other if the values
are within a Cache Writeback Granule (CWG) of each other.
Collect the data into two sections .mmuoff.data.read and .mmuoff.data.write,
the linker script ensures mmuoff.data.write section is aligned to the
architectural maximum CWG of 2KB.

Signed-off-by: James Morse <james.morse@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 15 insertions, 10 deletions

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 2196762..9ee9666 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -463,7 +463,7 @@ ENDPROC(__primary_switched)
  * end early head section, begin head code that is also used for
  * hotplug and needs to have the same protections as the text region
  */
-	.section ".text","ax"
+	.section ".idmap.text","ax"
 
 ENTRY(kimage_vaddr)
 	.quad		_text - TEXT_OFFSET
@@ -619,17 +619,29 @@ set_cpu_boot_mode_flag:
 ENDPROC(set_cpu_boot_mode_flag)
 
 /*
+ * These values are written with the MMU off, but read with the MMU on.
+ * Writers will invalidate the corresponding address, discarding up to a
+ * 'Cache Writeback Granule' (CWG) worth of data. The linker script ensures
+ * sufficient alignment that the CWG doesn't overlap another section.
+ */
+	.pushsection ".mmuoff.data.write", "aw"
+/*
  * We need to find out the CPU boot mode long after boot, so we need to
  * store it in a writable variable.
  *
  * This is not in .bss, because we set it sufficiently early that the boot-time
  * zeroing of .bss would clobber it.
  */
-	.pushsection	.data..cacheline_aligned
-	.align	L1_CACHE_SHIFT
 ENTRY(__boot_cpu_mode)
 	.long	BOOT_CPU_MODE_EL2
 	.long	BOOT_CPU_MODE_EL1
+/*
+ * The booting CPU updates the failed status @__early_cpu_boot_status,
+ * with MMU turned off.
+ */
+ENTRY(__early_cpu_boot_status)
+	.long 	0
+
 	.popsection
 
 	/*
@@ -702,12 +714,6 @@ ENDPROC(__secondary_switched)
 	dc	ivac, \tmp1			// Invalidate potentially stale cache line
 	.endm
 
-	.pushsection	.data..cacheline_aligned
-	.align	L1_CACHE_SHIFT
-ENTRY(__early_cpu_boot_status)
-	.long 	0
-	.popsection
-
 /*
  * Enable the MMU.
  *
@@ -719,7 +725,6 @@ ENTRY(__early_cpu_boot_status)
  * Checks if the selected granule size is supported by the CPU.
  * If it isn't, park the CPU
  */
-	.section	".idmap.text", "ax"
 ENTRY(__enable_mmu)
 	mrs	x22, sctlr_el1			// preserve old SCTLR_EL1 value
 	mrs	x1, ID_AA64MMFR0_EL1