linux-kernel - [RFC PATCH] arch: arm64: have memblocks out of kernel text use section map

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Date:   Fri, 12 Nov 2021 17:20:42 +0800
From:   Huangzhaoyang <huangzhaoyang@...il.com>
To:     Ard Biesheuvel <ardb@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Jonathan Marek <jonathan@...ek.ca>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [RFC PATCH] arch: arm64: have memblocks out of kernel text use section map

From: Zhaoyang Huang <zhaoyang.huang@...soc.com>

By comparing the swapper_pg_dir with k54 and previous versions,we find
that the linear mappings within which the addr is out of kernel text section
will use the smallest pte. It should arise for the sake of rodata_full, which
set all memblock use NO_CONT_MAPPINGS.

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
---
 arch/arm64/mm/mmu.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index cfd9deb..14e1bea 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -252,6 +252,8 @@ static void init_pmd(pud_t *pudp, unsigned long addr, unsigned long end,
 	pmd_clear_fixmap();
 }
 
+static bool crash_mem_map __initdata;
+
 static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr,
 				unsigned long end, phys_addr_t phys,
 				pgprot_t prot,
@@ -259,7 +261,15 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr,
 {
 	unsigned long next;
 	pud_t pud = READ_ONCE(*pudp);
+	unsigned long len = end - addr;
+	phys_addr_t kernel_start = __pa_symbol(_stext);
+	phys_addr_t kernel_end = __pa_symbol(__init_begin);
 
+	if (debug_pagealloc_enabled() || crash_mem_map || IS_ENABLED(CONFIG_KFENCE))
+		;
+	else if (phys > kernel_end || phys + len < kernel_start) {
+		flags &= ~(NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS);
+	}
 	/*
 	 * Check for initial section mappings in the pgd/pud.
 	 */
@@ -483,7 +493,6 @@ void __init mark_linear_text_alias_ro(void)
 			    PAGE_KERNEL_RO);
 }
 
-static bool crash_mem_map __initdata;
 
 static int __init enable_crash_mem_map(char *arg)
 {
-- 
1.9.1