linux-kernel - [PATCH 2/3] arm64: kdump: use page-level mapping for crashkernel region

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Date:   Fri, 21 Jul 2023 16:17:25 +0800
From:   thunder.leizhen@...weicloud.com
To:     Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Zhen Lei <thunder.leizhen@...wei.com>
Subject: [PATCH 2/3] arm64: kdump: use page-level mapping for crashkernel region

From: Zhen Lei <thunder.leizhen@...wei.com>

Use page-level mappings for crashkernel region so that we can use
set_memory_valid() to do access protection for it.

Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
---
 arch/arm64/mm/mmu.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 95d360805f8aeb3..e0a197ebe14837d 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -594,6 +594,11 @@ static void __init map_mem(pgd_t *pgdp)
 	 */
 	memblock_mark_nomap(kernel_start, kernel_end - kernel_start);
 
+#ifdef CONFIG_KEXEC_CORE
+	if (crashk_res.end)
+		memblock_mark_nomap(crashk_res.start, resource_size(&crashk_res));
+#endif
+
 	/* map all the memory banks */
 	for_each_mem_range(i, &start, &end) {
 		if (start >= end)
@@ -621,6 +626,22 @@ static void __init map_mem(pgd_t *pgdp)
 		       PAGE_KERNEL, NO_CONT_MAPPINGS);
 	memblock_clear_nomap(kernel_start, kernel_end - kernel_start);
 	arm64_kfence_map_pool(early_kfence_pool, pgdp);
+
+	/*
+	 * Use page-level mappings here so that we can shrink the region
+	 * in page granularity and put back unused memory to buddy system
+	 * through /sys/kernel/kexec_crash_size interface.
+	 */
+#ifdef CONFIG_KEXEC_CORE
+	if (crashk_res.end) {
+		__map_memblock(pgdp, crashk_res.start,
+			       crashk_res.end + 1,
+			       PAGE_KERNEL,
+			       NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS);
+		memblock_clear_nomap(crashk_res.start,
+				     resource_size(&crashk_res));
+	}
+#endif
 }
 
 void mark_rodata_ro(void)
-- 
2.25.1