Hi Henry,
Title: NIT: Add () after _mm to stay consistent with the rest.
On 01/08/2023 04:44, Henry Wang wrote:
From: Wei Chen <wei.c...@arm.com>
At the moment, on MMU system, enable_mmu() will return to an
address in the 1:1 mapping, then each path is responsible to
switch to virtual runtime mapping. Then remove_identity_mapping()
is called on the boot CPU to remove all 1:1 mapping.
Since remove_identity_mapping() is not necessary on Non-MMU system,
and we also avoid creating empty function for Non-MMU system, trying
to keep only one codeflow in arm64/head.S, we move path switch and
remove_identity_mapping() in enable_mmu() on MMU system.
As the remove_identity_mapping should only be called for the boot
CPU only, so we introduce enable_boot_cpu_mm() for boot CPU and
enable_secondary_cpu_mm() for secondary CPUs in this patch.
Signed-off-by: Wei Chen <wei.c...@arm.com>
Signed-off-by: Penny Zheng <penny.zh...@arm.com>
Signed-off-by: Henry Wang <henry.w...@arm.com>
---
v4:
- Clarify remove_identity_mapping() is called on boot CPU and keep
the function/proc format consistent in commit msg.
- Drop inaccurate (due to the refactor) in-code comment.
- Rename enable_{boot,runtime}_mmu to enable_{boot,secondary}_cpu_mm.
- Reword the in-code comment on top of enable_{boot,secondary}_cpu_mm.
- Call "fail" for unreachable code.
v3:
- new patch
---
xen/arch/arm/arm64/head.S | 89 ++++++++++++++++++++++++++++++---------
1 file changed, 70 insertions(+), 19 deletions(-)
diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 31cdb54d74..2af9f974d5 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -313,21 +313,11 @@ real_start_efi:
bl check_cpu_mode
bl cpu_init
- bl create_page_tables
- load_paddr x0, boot_pgtable
- bl enable_mmu
- /* We are still in the 1:1 mapping. Jump to the runtime Virtual Address. */
- ldr x0, =primary_switched
- br x0
+ ldr lr, =primary_switched
+ b enable_boot_cpu_mm
+
primary_switched:
- /*
- * The 1:1 map may clash with other parts of the Xen virtual memory
- * layout. As it is not used anymore, remove it completely to
- * avoid having to worry about replacing existing mapping
- * afterwards.
- */
- bl remove_identity_mapping
bl setup_fixmap
#ifdef CONFIG_EARLY_PRINTK
/* Use a virtual address to access the UART. */
@@ -372,13 +362,10 @@ GLOBAL(init_secondary)
#endif
bl check_cpu_mode
bl cpu_init
- load_paddr x0, init_ttbr
- ldr x0, [x0]
- bl enable_mmu
- /* We are still in the 1:1 mapping. Jump to the runtime Virtual Address. */
- ldr x0, =secondary_switched
- br x0
+ ldr lr, =secondary_switched
+ b enable_secondary_cpu_mm
+
secondary_switched:
#ifdef CONFIG_EARLY_PRINTK
/* Use a virtual address to access the UART. */
@@ -737,6 +724,70 @@ enable_mmu:
ret
ENDPROC(enable_mmu)
+/*
+ * Enable mm (turn on the data cache and the MMU) for secondary CPUs.
+ * The function will return to the virtual address provided in LR (e.g. the
+ * runtime mapping).
+ *
+ * Inputs:
+ * lr : Virtual address to return to.
+ *
+ * Clobbers x0 - x5
+ */
+enable_secondary_cpu_mm:
+ mov x5, lr
+
+ load_paddr x0, init_ttbr
+ ldr x0, [x0]
+
+ bl enable_mmu
+ mov lr, x5
+
+ /* return to secondary_switched */
Technically, you will return to the virtual address set in 'lr'. This is
'secondary_switched' today but this could change.
So it would be better to have a more generic comment like:
Return to the virtual address requested by the caller.
+ ret
+ENDPROC(enable_secondary_cpu_mm)
+
+/*
+ * Enable mm (turn on the data cache and the MMU) for the boot CPU.
+ * The function will return to the virtual address provided in LR (e.g. the
+ * runtime mapping).
+ *
+ * Inputs:
+ * lr : Virtual address to return to.
+ *
+ * Clobbers x0 - x5
+ */
+enable_boot_cpu_mm:
+ mov x5, lr
+
+ bl create_page_tables
+ load_paddr x0, boot_pgtable
+
+ bl enable_mmu
+ mov lr, x5
+
+ /*
+ * The MMU is turned on and we are in the 1:1 mapping. Switch
+ * to the runtime mapping.
+ */
+ ldr x0, =1f
+ br x0
+1:
+ /*
+ * The 1:1 map may clash with other parts of the Xen virtual memory
+ * layout. As it is not used anymore, remove it completely to
+ * avoid having to worry about replacing existing mapping
+ * afterwards. Function will return to primary_switched.
Same remark here.
+ */
+ b remove_identity_mapping
+
+ /*
+ * Below is supposed to be unreachable code, as "ret" in
+ * remove_identity_mapping will use the return address in LR in
advance.
+ */
+ b fail
Looking at this again, I am not entirely sure how this could reached if
remove_identity_mapping use 'ret' and you call it with 'b'. So I would
suggest to drop it and move 'mov lr, x5' closer to 'b
remove_identity_mapping'. So it is clearer that it will return.
+ENDPROC(enable_boot_cpu_mm)
+
/*
* Remove the 1:1 map from the page-tables. It is not easy to keep track
* where the 1:1 map was mapped, so we will look for the top-level entry
Cheers,
--
Julien Grall
