On Tue, 18 May 2021 at 17:53, Mark Rutland [off-list ref] wrote:

On Mon, May 17, 2021 at 08:51:12AM +0100, Fuad Tabba wrote:

quoted

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@arm.com>
Reported-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/linux-arch/20200511110014.lb9PEahJ4hVOYrbwIb_qUHXyNy9KQzNFdb_I3YlzY6A@z/
Signed-off-by: Fuad Tabba <redacted>
---
 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.
+      */

Minor nit, but the I-cache is *always* on (SCTLR.I affects the
attributes used for fetches into the I-caches), so it would be slightly
better to drop the "and I-cache on" words.

This may be true, but it may not be obvious to someone reading the
'MMU off' part of the comment. Bottom line is that we will be running
in a mode where we may hit in the I-cache, so it needs to be
invalidated. If we miss in the I-cache, we should fetch from the PoC,
hence the D-cache clean.

Otherwise, this looks good to me.

Mark.

quoted

      __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

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