linux-kernel - Re: [PATCH v4 1/3] amr64: map FDT as RW for early_init_dt

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Date:   Thu, 23 May 2019 17:04:18 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Hsin-Yi Wang <hsinyi@...omium.org>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Frank Rowand <frowand.list@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Miles Chen <miles.chen@...iatek.com>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        James Morse <james.morse@....com>,
        Andrew Murray <andrew.murray@....com>,
        Mark Rutland <mark.rutland@....com>,
        Jun Yao <yaojun8558363@...il.com>, Yu Zhao <yuzhao@...gle.com>,
        Robin Murphy <robin.murphy@....com>,
        Laura Abbott <labbott@...hat.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v4 1/3] amr64: map FDT as RW for early_init_dt_scan()

Quoting Hsin-Yi Wang (2019-05-19 09:04:44)
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index a170c6369a68..29648e86f7e5 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -940,12 +940,12 @@ void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot)
>         return dt_virt;
>  }
>  
> -void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
> +void *__init fixmap_remap_fdt(phys_addr_t dt_phys, pgprot_t prot)
>  {
>         void *dt_virt;
>         int size;
>  
> -       dt_virt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL_RO);
> +       dt_virt = __fixmap_remap_fdt(dt_phys, &size, prot);
>         if (!dt_virt)
>                 return NULL;
>  

Sorry, I'm still confused why we want to call memblock_reserve() again.
Why not avoid it?

diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index 67ef25d037ea..d0d9de9da5c1 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -137,7 +137,7 @@ extern void init_mem_pgprot(void);
 extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
 			       unsigned long virt, phys_addr_t size,
 			       pgprot_t prot, bool page_mappings_only);
-extern void *fixmap_remap_fdt(phys_addr_t dt_phys);
+extern void *__fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot);
 extern void mark_linear_text_alias_ro(void);
 
 #define INIT_MM_CONTEXT(name)	\
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index b09b6f75f759..0701c2cf1534 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c
@@ -65,9 +65,6 @@ static __init const u8 *kaslr_get_cmdline(void *fdt)
 	return default_cmdline;
 }
 
-extern void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size,
-				       pgprot_t prot);
-
 /*
  * This routine will be executed with the kernel mapped at its default virtual
  * address, and if it returns successfully, the kernel will be remapped, and
diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 413d566405d1..3e97354566ff 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -181,9 +181,13 @@ static void __init smp_build_mpidr_hash(void)
 
 static void __init setup_machine_fdt(phys_addr_t dt_phys)
 {
-	void *dt_virt = fixmap_remap_fdt(dt_phys);
+	int size;
+	void *dt_virt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL);
 	const char *name;
 
+	if (dt_virt)
+		memblock_reserve(dt_phys, size);
+
 	if (!dt_virt || !early_init_dt_scan(dt_virt)) {
 		pr_crit("\n"
 			"Error: invalid device tree blob at physical address %pa (virtual address 0x%p)\n"
@@ -195,6 +199,9 @@ static void __init setup_machine_fdt(phys_addr_t dt_phys)
 			cpu_relax();
 	}
 
+	/* Early fixups are done, map the FDT as read-only now */
+	__fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL_RO);
+
 	name = of_flat_dt_get_machine_name();
 	if (!name)
 		return;
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index a170c6369a68..ddf6086cd9dd 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -940,19 +940,6 @@ void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot)
 	return dt_virt;
 }
 
-void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
-{
-	void *dt_virt;
-	int size;
-
-	dt_virt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL_RO);
-	if (!dt_virt)
-		return NULL;
-
-	memblock_reserve(dt_phys, size);
-	return dt_virt;
-}
-
 int __init arch_ioremap_pud_supported(void)
 {
 	/* only 4k granule supports level 1 block mappings */