linux-kernel - [PATCH V4 1/3] riscv: mm: Prepare for reusing PTE RSW bit(9)

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Message-Id: <20240815030403.832489-2-zhangchunyan@iscas.ac.cn>
Date: Thu, 15 Aug 2024 11:04:01 +0800
From: Chunyan Zhang <zhangchunyan@...as.ac.cn>
To: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexandre Ghiti <alex@...ti.fr>
Cc: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Chunyan Zhang <zhang.lyra@...il.com>
Subject: [PATCH V4 1/3] riscv: mm: Prepare for reusing PTE RSW bit(9)

The PTE bit(9) on RISC-V is reserved for software, it is used by DEVMAP
now which has to be disabled if we want to use bit(9) for other features,
since there's no more free PTE bit on RISC-V now.

So to make ARCH_HAS_PTE_DEVMAP selectable, this patch uses it as
the build condition of devmap definitions.

Signed-off-by: Chunyan Zhang <zhangchunyan@...as.ac.cn>
---
 arch/riscv/include/asm/pgtable-64.h   | 2 +-
 arch/riscv/include/asm/pgtable-bits.h | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/pgtable-64.h b/arch/riscv/include/asm/pgtable-64.h
index 0897dd99ab8d..babb8d2b0f0b 100644
--- a/arch/riscv/include/asm/pgtable-64.h
+++ b/arch/riscv/include/asm/pgtable-64.h
@@ -398,7 +398,7 @@ static inline struct page *pgd_page(pgd_t pgd)
 #define p4d_offset p4d_offset
 p4d_t *p4d_offset(pgd_t *pgd, unsigned long address);
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && defined(CONFIG_ARCH_HAS_PTE_DEVMAP)
 static inline int pte_devmap(pte_t pte);
 static inline pte_t pmd_pte(pmd_t pmd);
 
diff --git a/arch/riscv/include/asm/pgtable-bits.h b/arch/riscv/include/asm/pgtable-bits.h
index a8f5205cea54..5bcc73430829 100644
--- a/arch/riscv/include/asm/pgtable-bits.h
+++ b/arch/riscv/include/asm/pgtable-bits.h
@@ -19,7 +19,13 @@
 #define _PAGE_SOFT      (3 << 8)    /* Reserved for software */
 
 #define _PAGE_SPECIAL   (1 << 8)    /* RSW: 0x1 */
+
+#ifdef CONFIG_ARCH_HAS_PTE_DEVMAP
 #define _PAGE_DEVMAP    (1 << 9)    /* RSW, devmap */
+#else
+#define _PAGE_DEVMAP	0
+#endif /* CONFIG_ARCH_HAS_PTE_DEVMAP */
+
 #define _PAGE_TABLE     _PAGE_PRESENT
 
 /*
-- 
2.34.1