[Xen-devel] [PATCH v3 13/28] xen/arm32: head: Introduce distinct paths for the boot CPU and secondary CPUs

[Julien Grall <julien.grall@arm.com>]

The boot code is currently quite difficult to go through because of the
lack of documentation and a number of indirection to avoid executing
some path in either the boot CPU or secondary CPUs.

In an attempt to make the boot code easier to follow, each parts of the
boot are now in separate functions. Furthermore, the paths for the boot
CPU and secondary CPUs are now distinct and for now will call each
functions.

Follow-ups will remove unnecessary calls and do further improvement
(such as adding documentation and reshuffling).

Note that the switch from using the ID mapping to the runtime mapping
is duplicated for each path. This is because in the future we will need
to stay longer in the ID mapping for the boot CPU.

Lastly, it is now required to save lr in cpu_init() becauswe the
function will call other functions and therefore clobber lr.

Signed-off-by: Julien Grall <julien.grall@arm.com>

---
    Changes in v3:
        - Remove hard tab
        - s/ID map/1:1 mapping/

    Changes in v2:
        - Patch added
---
 xen/arch/arm/arm32/head.S | 65 +++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 54 insertions(+), 11 deletions(-)

diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index c4ee06ba93..4285f76463 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -148,7 +148,19 @@ past_zImage:
 
         mov   r12, #0                /* r12 := is_secondary_cpu */
 
-        b     common_start
+        bl    check_cpu_mode
+        bl    zero_bss
+        bl    cpu_init
+        bl    create_page_tables
+        bl    enable_mmu
+
+        /* We are still in the 1:1 mapping. Jump to the runtime Virtual Address. */
+        ldr   r0, =primary_switched
+        mov   pc, r0
+primary_switched:
+        bl    setup_fixmap
+        b     launch
+ENDPROC(start)
 
 GLOBAL(init_secondary)
         cpsid aif                    /* Disable all interrupts */
@@ -179,8 +191,22 @@ GLOBAL(init_secondary)
         print_reg r7
         PRINT(" booting -\r\n")
 #endif
-
-common_start:
+        bl    check_cpu_mode
+        bl    zero_bss
+        bl    cpu_init
+        bl    create_page_tables
+        bl    enable_mmu
+
+
+        /* We are still in the 1:1 mapping. Jump to the runtime Virtual Address. */
+        ldr   r0, =secondary_switched
+        mov   pc, r0
+secondary_switched:
+        bl    setup_fixmap
+        b     launch
+ENDPROC(init_secondary)
+
+check_cpu_mode:
         /* Check that this CPU has Hyp mode */
         mrc   CP32(r0, ID_PFR1)
         and   r0, r0, #0xf000        /* Bits 12-15 define virt extensions */
@@ -202,7 +228,10 @@ common_start:
         b     fail
 
 hyp:    PRINT("- Xen starting in Hyp mode -\r\n")
+        mov   pc, lr
+ENDPROC(check_cpu_mode)
 
+zero_bss:
         /* Zero BSS On the boot CPU to avoid nasty surprises */
         teq   r12, #0
         bne   skip_bss
@@ -219,8 +248,14 @@ hyp:    PRINT("- Xen starting in Hyp mode -\r\n")
         blo   1b
 
 skip_bss:
+        mov   pc, lr
+ENDPROC(zero_bss)
+
+cpu_init:
         PRINT("- Setting up control registers -\r\n")
 
+        mov   r5, lr                       /* r5 := return address */
+
         /* Get processor specific proc info into r1 */
         bl    __lookup_processor_type
         teq   r1, #0
@@ -231,7 +266,6 @@ skip_bss:
         PRINT(" -\r\n")
         b     fail
 1:
-
         /* Jump to cpu_init */
         ldr   r1, [r1, #PROCINFO_cpu_init]  /* r1 := vaddr(init func) */
         adr   lr, cpu_init_done             /* Save return address */
@@ -256,6 +290,10 @@ cpu_init_done:
         ldr   r0, =HSCTLR_SET
         mcr   CP32(r0, HSCTLR)
 
+        mov   pc, r5                        /* Return address is in r5 */
+ENDPROC(cpu_init)
+
+create_page_tables:
         /*
          * Rebuild the boot pagetable's first-level entries. The structure
          * is described in mm.c.
@@ -359,15 +397,16 @@ cpu_init_done:
         /* boot pagetable setup complete */
 
         cmp   r6, #1                /* Did we manage to create an identity mapping ? */
-        beq   1f
+        moveq pc, lr
         PRINT("Unable to build boot page tables - Failed to identity map Xen.\r\n")
         b     fail
 virtphys_clash:
         /* Identity map clashes with boot_third, which we cannot handle yet */
         PRINT("- Unable to build boot page tables - virt and phys addresses clash. -\r\n")
         b     fail
+ENDPROC(create_page_tables)
 
-1:
+enable_mmu:
         PRINT("- Turning on paging -\r\n")
 
         /*
@@ -377,16 +416,16 @@ virtphys_clash:
         mcr   CP32(r0, TLBIALLH)     /* Flush hypervisor TLBs */
         dsb   nsh
 
-        ldr   r1, =paging            /* Explicit vaddr, not RIP-relative */
         mrc   CP32(r0, HSCTLR)
         /* Enable MMU and D-cache */
         orr   r0, r0, #(SCTLR_Axx_ELx_M|SCTLR_Axx_ELx_C)
         dsb                          /* Flush PTE writes and finish reads */
         mcr   CP32(r0, HSCTLR)       /* now paging is enabled */
         isb                          /* Now, flush the icache */
-        mov   pc, r1                 /* Get a proper vaddr into PC */
-paging:
+        mov   pc, lr
+ENDPROC(enable_mmu)
 
+setup_fixmap:
         /*
          * Now we can install the fixmap and dtb mappings, since we
          * don't need the 1:1 map any more
@@ -436,12 +475,15 @@ paging:
         mcr   CP32(r0, TLBIALLH)     /* Flush hypervisor TLB */
         dsb                          /* Ensure completion of TLB flush */
         isb
+        mov   pc, lr
+ENDPROC(setup_fixmap)
 
+launch:
         PRINT("- Ready -\r\n")
 
         /* The boot CPU should go straight into C now */
         teq   r12, #0
-        beq   launch
+        beq   1f
 
         /*
          * Non-boot CPUs need to move on to the proper pagetables, which were
@@ -460,7 +502,7 @@ paging:
         dsb                          /* Ensure completion of TLB+BP flush */
         isb
 
-launch:
+1:
         ldr   r0, =init_data
         add   r0, #INITINFO_stack    /* Find the boot-time stack */
         ldr   sp, [r0]
@@ -471,6 +513,7 @@ launch:
         moveq r1, r8                 /*               - DTB address */
         beq   start_xen              /* and disappear into the land of C */
         b     start_secondary        /* (to the appropriate entry point) */
+ENDPROC(launch)
 
 /* Fail-stop */
 fail:   PRINT("- Boot failed -\r\n")
-- 
2.11.0


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