Re: [PATCH] arm64/mm: Fix idmap on [16K|36VA|48PA]
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2021-08-03 10:35:04
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On Mon, Aug 02, 2021 at 10:12:39AM +0530, Anshuman Khandual wrote:
When creating the idmap, the kernel may add one extra level to idmap memory outside the VA range. But for [16K|36VA|48PA], we need two levels to reach 48 bits. If the bootloader places the kernel in memory above (1 << 46), the
Did you mean (1 << 36)?
kernel will fail to enable the MMU. Although we are not aware of a platform where this happens, it is worth to accommodate such scenarios and prevent a possible kernel crash. Lets fix the problem on the above configuration by creating two additional idmap page table levels when 'idmap_text_end' is outside the VA range. This reduces 'idmap_t0sz' to cover the entire PA range which would prevent table misconfiguration (fault) when a given 'idmap_t0sz' value requires a single additional page table level where as two have been built.
[...]
quoted hunk ↗ jump to hunk
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index c5c994a..da33bbc 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S@@ -329,7 +329,9 @@ SYM_FUNC_START_LOCAL(__create_page_tables) #if (VA_BITS < 48) #define EXTRA_SHIFT (PGDIR_SHIFT + PAGE_SHIFT - 3) +#define EXTRA_SHIFT_1 (EXTRA_SHIFT + PAGE_SHIFT - 3) #define EXTRA_PTRS (1 << (PHYS_MASK_SHIFT - EXTRA_SHIFT)) +#define EXTRA_PTRS_1 (1 << (PHYS_MASK_SHIFT - EXTRA_SHIFT_1)) /* * If VA_BITS < 48, we have to configure an additional table level.@@ -342,8 +344,30 @@ SYM_FUNC_START_LOCAL(__create_page_tables) #error "Mismatch between VA_BITS and page size/number of translation levels" #endif +/* + * In this particular CONFIG_ARM64_16K_PAGES config, there might be a + * scenario where 'idmap_text_end' ends up high enough in the PA range + * requiring two additional idmap page table levels. Reduce idmap_t0sz + * to cover the entire PA range. This prevents table misconfiguration + * when a given idmap_t0sz value just requires single additional level + * where as two levels have been built. + */ +#if defined(CONFIG_ARM64_VA_BITS_36) && defined(CONFIG_ARM64_PA_BITS_48) + mov x4, EXTRA_PTRS_1 + create_table_entry x0, x3, EXTRA_SHIFT_1, x4, x5, x6 + + mov x4, PTRS_PER_PTE + create_table_entry x0, x3, EXTRA_SHIFT, x4, x5, x6 + + mov x5, #64 - PHYS_MASK_SHIFT + adr_l x6, idmap_t0sz + str x5, [x6] + dmb sy + dc ivac, x6 +#else mov x4, EXTRA_PTRS create_table_entry x0, x3, EXTRA_SHIFT, x4, x5, x6 +#endif #else /* * If VA_BITS == 48, we don't have to configure an additional
There's a prior idmap_t0sz setting based on __idmap_text_end. Isn't that sufficient? We don't care about covering the whole PA space, just the __idmap_text_end. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel