arm64: head: record CPU boot mode after enabling the MMU

In order to avoid having to touch memory with the MMU and caches
disabled, and therefore having to invalidate it from the caches
explicitly, just defer storing the value until after the MMU has been
turned on, unless we are giving up with an error.

While at it, move the associated variable definitions into C code.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20220624150651.1358849-19-ardb@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 583cbea..8de346d 100644 (file)
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -82,6 +82,7 @@
         * primary lowlevel boot path:
         *
         *  Register   Scope                      Purpose
+        *  x20        primary_entry() .. __primary_switch()    CPU boot mode
         *  x21        primary_entry() .. start_kernel()        FDT pointer passed at boot in x0
         *  x22        create_idmap() .. start_kernel()         ID map VA of the DT blob
         *  x23        primary_entry() .. start_kernel()        physical misalignment/KASLR offset
@@ -91,9 +92,9 @@
 SYM_CODE_START(primary_entry)
        bl      preserve_boot_args
        bl      init_kernel_el                  // w0=cpu_boot_mode
+       mov     x20, x0
        adrp    x23, __PHYS_OFFSET
        and     x23, x23, MIN_KIMG_ALIGN - 1    // KASLR offset, defaults to 0
-       bl      set_cpu_boot_mode_flag
        bl      create_idmap
 
        /*
@@ -429,6 +430,9 @@ SYM_FUNC_START_LOCAL(__primary_switched)
        sub     x4, x4, x0                      // the kernel virtual and
        str_l   x4, kimage_voffset, x5          // physical mappings
 
+       mov     x0, x20
+       bl      set_cpu_boot_mode_flag
+
        // Clear BSS
        adr_l   x0, __bss_start
        mov     x1, xzr
@@ -454,6 +458,7 @@ SYM_FUNC_START_LOCAL(__primary_switched)
        ret                                     // to __primary_switch()
 0:
 #endif
+       mov     x0, x20
        bl      switch_to_vhe                   // Prefer VHE if possible
        ldp     x29, x30, [sp], #16
        bl      start_kernel
@@ -553,52 +558,21 @@ SYM_FUNC_START_LOCAL(set_cpu_boot_mode_flag)
        b.ne    1f
        add     x1, x1, #4
 1:     str     w0, [x1]                        // Save CPU boot mode
-       dmb     sy
-       dc      ivac, x1                        // Invalidate potentially stale cache line
        ret
 SYM_FUNC_END(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.
- */
-SYM_DATA_START(__boot_cpu_mode)
-       .long   BOOT_CPU_MODE_EL2
-       .long   BOOT_CPU_MODE_EL1
-SYM_DATA_END(__boot_cpu_mode)
-/*
- * The booting CPU updates the failed status @__early_cpu_boot_status,
- * with MMU turned off.
- */
-SYM_DATA_START(__early_cpu_boot_status)
-       .quad   0
-SYM_DATA_END(__early_cpu_boot_status)
-
-       .popsection
-
        /*
         * This provides a "holding pen" for platforms to hold all secondary
         * cores are held until we're ready for them to initialise.
         */
 SYM_FUNC_START(secondary_holding_pen)
        bl      init_kernel_el                  // w0=cpu_boot_mode
-       bl      set_cpu_boot_mode_flag
-       mrs     x0, mpidr_el1
+       mrs     x2, mpidr_el1
        mov_q   x1, MPIDR_HWID_BITMASK
-       and     x0, x0, x1
+       and     x2, x2, x1
        adr_l   x3, secondary_holding_pen_release
 pen:   ldr     x4, [x3]
-       cmp     x4, x0
+       cmp     x4, x2
        b.eq    secondary_startup
        wfe
        b       pen
@@ -610,7 +584,6 @@ SYM_FUNC_END(secondary_holding_pen)
         */
 SYM_FUNC_START(secondary_entry)
        bl      init_kernel_el                  // w0=cpu_boot_mode
-       bl      set_cpu_boot_mode_flag
        b       secondary_startup
 SYM_FUNC_END(secondary_entry)
 
@@ -618,6 +591,7 @@ SYM_FUNC_START_LOCAL(secondary_startup)
        /*
         * Common entry point for secondary CPUs.
         */
+       mov     x20, x0                         // preserve boot mode
        bl      switch_to_vhe
        bl      __cpu_secondary_check52bitva
        bl      __cpu_setup                     // initialise processor
@@ -629,6 +603,9 @@ SYM_FUNC_START_LOCAL(secondary_startup)
 SYM_FUNC_END(secondary_startup)
 
 SYM_FUNC_START_LOCAL(__secondary_switched)
+       mov     x0, x20
+       bl      set_cpu_boot_mode_flag
+       str_l   xzr, __early_cpu_boot_status, x3
        adr_l   x5, vectors
        msr     vbar_el1, x5
        isb
@@ -691,7 +668,6 @@ SYM_FUNC_START(__enable_mmu)
        b.lt    __no_granule_support
        cmp     x3, #ID_AA64MMFR0_TGRAN_SUPPORTED_MAX
        b.gt    __no_granule_support
-       update_early_cpu_boot_status 0, x3, x4
        phys_to_ttbr x2, x2
        msr     ttbr0_el1, x2                   // load TTBR0
        load_ttbr1 x1, x1, x3

diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
index 43d2126..5bafb53 100644 (file)
--- a/arch/arm64/kernel/hyp-stub.S
+++ b/arch/arm64/kernel/hyp-stub.S
@@ -223,11 +223,11 @@ SYM_FUNC_END(__hyp_reset_vectors)
 
 /*
  * Entry point to switch to VHE if deemed capable
+ *
+ * w0: boot mode, as returned by init_kernel_el()
  */
 SYM_FUNC_START(switch_to_vhe)
        // Need to have booted at EL2
-       adr_l   x1, __boot_cpu_mode
-       ldr     w0, [x1]
        cmp     w0, #BOOT_CPU_MODE_EL2
        b.ne    1f
 

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index fd558cf..05d77f2 100644 (file)
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -56,6 +56,14 @@ EXPORT_SYMBOL(kimage_vaddr);
 u64 kimage_voffset __ro_after_init;
 EXPORT_SYMBOL(kimage_voffset);
 
+u32 __boot_cpu_mode[] = { BOOT_CPU_MODE_EL2, BOOT_CPU_MODE_EL1 };
+
+/*
+ * The booting CPU updates the failed status @__early_cpu_boot_status,
+ * with MMU turned off.
+ */
+long __section(".mmuoff.data.write") __early_cpu_boot_status;
+
 /*
  * Empty_zero_page is a special page that is used for zero-initialized data
  * and COW.