ARM, arm64: kvm: get rid of the bounce page

The HYP init bounce page is a runtime construct that ensures that the
HYP init code does not cross a page boundary. However, this is something
we can do perfectly well at build time, by aligning the code appropriately.

For arm64, we just align to 4 KB, and enforce that the code size is less
than 4 KB, regardless of the chosen page size.

For ARM, the whole code is less than 256 bytes, so we tweak the linker
script to align at a power of 2 upper bound of the code size

Note that this also fixes a benign off-by-one error in the original bounce
page code, where a bounce page would be allocated unnecessarily if the code
was exactly 1 page in size.

On ARM, it also fixes an issue with very large kernels reported by Arnd
Bergmann, where stub sections with linker emitted veneers could erroneously
trigger the size/alignment ASSERT() in the linker script.

Tested-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 15 insertions, 3 deletions

diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index b31aa73e8076..ba65f1217310 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -23,11 +23,20 @@
         VMLINUX_SYMBOL(__idmap_text_start) = .;                         \
         *(.idmap.text)                                                  \
         VMLINUX_SYMBOL(__idmap_text_end) = .;                           \
-        . = ALIGN(32);                                                  \
+        . = ALIGN(1 << LOG2CEIL(__hyp_idmap_size));                     \
         VMLINUX_SYMBOL(__hyp_idmap_text_start) = .;                     \
         *(.hyp.idmap.text)                                              \
         VMLINUX_SYMBOL(__hyp_idmap_text_end) = .;
 
+/*
+ * If the HYP idmap .text section is populated, it needs to be positioned
+ * such that it will not cross a page boundary in the final output image.
+ * So align it to the section size rounded up to the next power of 2.
+ * If __hyp_idmap_size is undefined, the section will be empty so define
+ * it as 0 in that case.
+ */
+PROVIDE(__hyp_idmap_size = 0);
+
 #ifdef CONFIG_HOTPLUG_CPU
 #define ARM_CPU_DISCARD(x)
 #define ARM_CPU_KEEP(x)         x
@@ -346,8 +355,11 @@ SECTIONS
  */
 ASSERT((__proc_info_end - __proc_info_begin), "missing CPU support")
 ASSERT((__arch_info_end - __arch_info_begin), "no machine record defined")
+
 /*
- * The HYP init code can't be more than a page long.
+ * The HYP init code can't be more than a page long,
+ * and should not cross a page boundary.
  * The above comment applies as well.
  */
-ASSERT(((__hyp_idmap_text_end - __hyp_idmap_text_start) <= PAGE_SIZE), "HYP init code too big")
+ASSERT((__hyp_idmap_text_start & ~PAGE_MASK) + __hyp_idmap_size <= PAGE_SIZE,
+        "HYP init code too big or misaligned")