The exception level in which the kernel was entered needs to be saved for
later. We do this by writing the exception level to memory. As this data
is written with the MMU/cache off it will bypass any cache, after this we
invalidate the address so that later reads from cacheable mappings do not
read a stale cache line. The side effect of this invalidate is any
existing cache line for this address in the same coherency domain will be
cleaned and written into memory, possibly overwriting the data we just
wrote. As this memory is treated as cacheable by already running cores it
on not architecturally safe to perform any non-caching accesses to this
memory anyway.
Lets avoid these issues altogether by moving the writing of the boot
exception level to after MMU/caching has been enabled. Saving the boot
state in unused register x22 until we can safely and coherently write out
this data.
As the data is not written with the MMU off anymore we move the variable
definition out of this section and into a regular C code data section.
Signed-off-by: Andrew F. Davis <a...@ti.com>
---
arch/arm64/kernel/head.S | 31 +++++++++++--------------------
arch/arm64/kernel/smp.c | 10 ++++++++++
2 files changed, 21 insertions(+), 20 deletions(-)
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 2cdacd1c141b..4c71493742c5 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -99,6 +99,7 @@ pe_header:
*
* Register Scope Purpose
* x21 stext() .. start_kernel() FDT pointer passed at boot in
x0
+ * x22 stext() .. start_kernel() exception level core was
booted
* x23 stext() .. start_kernel() physical misalignment/KASLR
offset
* x28 __create_page_tables() callee preserved temp register
* x19/x20 __primary_switch() callee preserved temp
registers
@@ -108,7 +109,6 @@ ENTRY(stext)
bl el2_setup // Drop to EL1, w0=cpu_boot_mode
adrp x23, __PHYS_OFFSET
and x23, x23, MIN_KIMG_ALIGN - 1 // KASLR offset, defaults to 0
- bl set_cpu_boot_mode_flag
bl __create_page_tables
/*
* The following calls CPU setup code, see arch/arm64/mm/proc.S for
@@ -428,6 +428,8 @@ __primary_switched:
sub x4, x4, x0 // the kernel virtual and
str_l x4, kimage_voffset, x5 // physical mappings
+ bl set_cpu_boot_mode_flag
+
// Clear BSS
adr_l x0, __bss_start
mov x1, xzr
@@ -470,7 +472,7 @@ EXPORT_SYMBOL(kimage_vaddr)
* If we're fortunate enough to boot at EL2, ensure that the world is
* sane before dropping to EL1.
*
- * Returns either BOOT_CPU_MODE_EL1 or BOOT_CPU_MODE_EL2 in w0 if
+ * Returns either BOOT_CPU_MODE_EL1 or BOOT_CPU_MODE_EL2 in w22 if
* booted in EL1 or EL2 respectively.
*/
ENTRY(el2_setup)
@@ -480,7 +482,7 @@ ENTRY(el2_setup)
b.eq 1f
mov_q x0, (SCTLR_EL1_RES1 | ENDIAN_SET_EL1)
msr sctlr_el1, x0
- mov w0, #BOOT_CPU_MODE_EL1 // This cpu booted in EL1
+ mov w22, #BOOT_CPU_MODE_EL1 // This cpu booted in EL1
isb
ret
@@ -593,7 +595,7 @@ set_hcr:
cbz x2, install_el2_stub
- mov w0, #BOOT_CPU_MODE_EL2 // This CPU booted in EL2
+ mov w22, #BOOT_CPU_MODE_EL2 // This CPU booted in EL2
isb
ret
@@ -632,7 +634,7 @@ install_el2_stub:
PSR_MODE_EL1h)
msr spsr_el2, x0
msr elr_el2, lr
- mov w0, #BOOT_CPU_MODE_EL2 // This CPU booted in EL2
+ mov w22, #BOOT_CPU_MODE_EL2 // This CPU booted in EL2
eret
ENDPROC(el2_setup)
@@ -642,12 +644,10 @@ ENDPROC(el2_setup)
*/
set_cpu_boot_mode_flag:
adr_l x1, __boot_cpu_mode
- cmp w0, #BOOT_CPU_MODE_EL2
+ cmp w22, #BOOT_CPU_MODE_EL2
b.ne 1f
- add x1, x1, #4
-1: str w0, [x1] // This CPU has booted in EL1
- dmb sy
- dc ivac, x1 // Invalidate potentially stale
cache line
+ add x1, x1, #4 // This CPU has booted in EL2
+1: str w22, [x1]
ret
ENDPROC(set_cpu_boot_mode_flag)
@@ -658,16 +658,7 @@ ENDPROC(set_cpu_boot_mode_flag)
* 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.
- */
-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.
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 018a33e01b0e..66bdcaf61a46 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -65,6 +65,16 @@ struct secondary_data secondary_data;
/* Number of CPUs which aren't online, but looping in kernel text. */
int cpus_stuck_in_kernel;
+/*
+ * We need to find out the CPU boot mode long after boot, so we need to
+ * store it in a writable variable in early boot. Any core started in
+ * EL1 will write that to the first location, EL2 to the second. After
+ * all cores are started this allows us to check that all cores started
+ * in the same mode.
+ */
+u32 __boot_cpu_mode[2] = { BOOT_CPU_MODE_EL2, BOOT_CPU_MODE_EL1 };
+EXPORT_SYMBOL(__boot_cpu_mode);
+
enum ipi_msg_type {
IPI_RESCHEDULE,
IPI_CALL_FUNC,
--
2.17.1
