linux-kernel - [PATCH 3/3] arm64: reduce trampoline data alignment

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Date:   Thu, 19 Mar 2020 11:14:07 +0200
From:   Rémi Denis-Courmont <remi@...lab.net>
To:     catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org
Cc:     mark.rutland@....com, james.morse@....com,
        linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] arm64: reduce trampoline data alignment

From: Rémi Denis-Courmont <remi.denis.courmont@...wei.com>

The trampoline data, currently consisting of two relocated pointers,
must be within a single page. However, there are no needs for it to
start a page.

This reduces the alignment to 16 bytes, which is sufficient to ensure
that the data is entirely within a single page of the fixmap.

Signed-off-by: Rémi Denis-Courmont <remi.denis.courmont@...wei.com>
---
 arch/arm64/kernel/entry.S | 2 +-
 arch/arm64/mm/mmu.c       | 5 ++---
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index c36733d8cd75..ecad15443655 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -858,7 +858,7 @@ SYM_CODE_END(tramp_exit_compat)
 	.popsection				// .entry.tramp.text
 #ifdef CONFIG_RANDOMIZE_BASE
 	.pushsection ".rodata", "a"
-	.align PAGE_SHIFT
+	.align	4	// all .rodata must be in a single fixmap page
 SYM_DATA_START(__entry_tramp_data_start)
 	.quad	vectors
 SYM_DATA_END(__entry_tramp_data_start)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 9b08f7c7e6f0..6a0e75f48e7b 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -599,9 +599,8 @@ static int __init map_entry_trampoline(void)
 	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
 		extern char __entry_tramp_data_start[];
 
-		__set_fixmap(FIX_ENTRY_TRAMP_DATA,
-			     __pa_symbol(__entry_tramp_data_start),
-			     PAGE_KERNEL_RO);
+		pa_start = __pa_symbol(__entry_tramp_data_start) & PAGE_MASK;
+		__set_fixmap(FIX_ENTRY_TRAMP_DATA, pa_start, PAGE_KERNEL_RO);
 	}
 
 	return 0;
-- 
2.26.0.rc2