From 55564814a838f1d2429dc757294df798f5262bd2 Mon Sep 17 00:00:00 2001 From: Ryan Roberts Date: Fri, 3 May 2024 15:46:01 +0100 Subject: [PATCH] arm64/mm: Move PTE_PRESENT_INVALID to overlay PTE_NG PTE_PRESENT_INVALID was previously occupying bit 59, which when a PTE is valid can either be IGNORED, PBHA[0] or AttrIndex[3], depending on the HW configuration. In practice this is currently not a problem because PTE_PRESENT_INVALID can only be 1 when PTE_VALID=0 and upstream Linux always requires the bit set to 0 for a valid pte. However, if in future Linux wants to use the field (e.g. AttrIndex[3]) then we could end up with confusion when PTE_PRESENT_INVALID comes along and corrupts the field - we would ideally want to preserve it even for an invalid (but present) pte. The other problem with bit 59 is that it prevents the offset field of a swap entry within a swap pte from growing beyond 51 bits. By moving PTE_PRESENT_INVALID to a low bit we can lay the swap pte out so that the offset field could grow to 52 bits in future. So let's move PTE_PRESENT_INVALID to overlay PTE_NG (bit 11). There is no need to persist NG for a present-invalid entry; it is always set for user mappings and is not used by SW to derive any state from the pte. PTE_NS was considered instead of PTE_NG, but it is RES0 for non-secure SW, so there is a chance that future architecture may allocate the bit and we may therefore need to persist that bit for present-invalid ptes. These are both marginal benefits, but make things a bit tidier in my opinion. Reviewed-by: Catalin Marinas Signed-off-by: Ryan Roberts Link: https://lore.kernel.org/r/20240503144604.151095-4-ryan.roberts@arm.com Signed-off-by: Will Deacon --- arch/arm64/include/asm/pgtable-prot.h | 2 +- arch/arm64/include/asm/pgtable.h | 12 ++++++------ 2 files changed, 7 insertions(+), 7 deletions(-) diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h index 81f07b44f7b8..35c9de13f7ed 100644 --- a/arch/arm64/include/asm/pgtable-prot.h +++ b/arch/arm64/include/asm/pgtable-prot.h @@ -24,7 +24,7 @@ * interpreted according to the HW layout by SW but any attempted HW access to * the address will result in a fault. pte_present() returns true. */ -#define PTE_PRESENT_INVALID (_AT(pteval_t, 1) << 59) /* only when !PTE_VALID */ +#define PTE_PRESENT_INVALID (PTE_NG) /* only when !PTE_VALID */ #define _PROT_DEFAULT (PTE_TYPE_PAGE | PTE_AF | PTE_SHARED) #define _PROT_SECT_DEFAULT (PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S) diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 300abbc0e67a..6c0e322211cb 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -1261,15 +1261,15 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma, * Encode and decode a swap entry: * bits 0-1: present (must be zero) * bits 2: remember PG_anon_exclusive - * bits 3-7: swap type - * bits 8-57: swap offset - * bit 59: PTE_PRESENT_INVALID (must be zero) + * bits 6-10: swap type + * bit 11: PTE_PRESENT_INVALID (must be zero) + * bits 12-61: swap offset */ -#define __SWP_TYPE_SHIFT 3 +#define __SWP_TYPE_SHIFT 6 #define __SWP_TYPE_BITS 5 -#define __SWP_OFFSET_BITS 50 #define __SWP_TYPE_MASK ((1 << __SWP_TYPE_BITS) - 1) -#define __SWP_OFFSET_SHIFT (__SWP_TYPE_BITS + __SWP_TYPE_SHIFT) +#define __SWP_OFFSET_SHIFT 12 +#define __SWP_OFFSET_BITS 50 #define __SWP_OFFSET_MASK ((1UL << __SWP_OFFSET_BITS) - 1) #define __swp_type(x) (((x).val >> __SWP_TYPE_SHIFT) & __SWP_TYPE_MASK)