[PATCH v2 04/16] arm64: Downgrade flush_icache_range to invalidate

[Fuad Tabba]

Since __flush_dcache_area is called right before,
invalidate_icache_range is sufficient in this case.

Rewrite the comment to better explain the rationale behind the
cache maintenance operations used here.

No functional change intended.
Possible performance impact due to invalidating only the icache
rather than invalidating and cleaning both caches.

Reported-by: Catalin Marinas <catalin.marinas at arm.com>
Reported-by: Will Deacon <will at kernel.org>
Link: https://lore.kernel.org/linux-arch/20200511110014.lb9PEahJ4hVOYrbwIb_qUHXyNy9KQzNFdb_I3YlzY6A@z/
Signed-off-by: Fuad Tabba <tabba at google.com>
---
 arch/arm64/kernel/machine_kexec.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
index 90a335c74442..ecd8915e02e1 100644
--- a/arch/arm64/kernel/machine_kexec.c
+++ b/arch/arm64/kernel/machine_kexec.c
@@ -68,10 +68,14 @@ int machine_kexec_post_load(struct kimage *kimage)
 	kimage->arch.kern_reloc = __pa(reloc_code);
 	kexec_image_info(kimage);
 
-	/* Flush the reloc_code in preparation for its execution. */
+	/*
+	 * For execution with the MMU off and I-cache on, reloc_code needs to be
+	 * cleaned to the PoC and invalidated from the I-cache.
+	 */
 	__flush_dcache_area(reloc_code, arm64_relocate_new_kernel_size);
-	flush_icache_range((uintptr_t)reloc_code, (uintptr_t)reloc_code +
-			   arm64_relocate_new_kernel_size);
+	invalidate_icache_range((uintptr_t)reloc_code,
+				(uintptr_t)reloc_code +
+					arm64_relocate_new_kernel_size);
 
 	return 0;
 }
-- 
2.31.1.751.gd2f1c929bd-goog