linux-kernel - [PATCH v4 1/5] riscv: pgtable: Use riscv_has_extension

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Message-Id: <20251020-riscv-altn-helper-wip-v4-1-ef941c87669a@iscas.ac.cn>
Date: Mon, 20 Oct 2025 17:09:56 +0800
From: Vivian Wang <wangruikang@...as.ac.cn>
To: Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Alexandre Ghiti <alex@...ti.fr>, Yury Norov <yury.norov@...il.com>, 
 Rasmus Villemoes <linux@...musvillemoes.dk>, Paul Walmsley <pjw@...nel.org>
Cc: Charlie Jenkins <charlie@...osinc.com>, 
 Xiao Wang <xiao.w.wang@...el.com>, 
 Christoph Müllner <christoph.muellner@...ll.eu>, 
 Vivian Wang <wangruikang@...as.ac.cn>, Vivian Wang <uwu@...m.page>, 
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v4 1/5] riscv: pgtable: Use riscv_has_extension_unlikely

Use riscv_has_extension_unlikely() to check for RISCV_ISA_EXT_SVVPTC,
replacing the use of asm goto with ALTERNATIVE.

The "unlikely" variant is used to match the behavior of the original
implementation using ALTERNATIVE("nop", "j %l[svvptc]", ...).

Note that this makes the check for RISCV_ISA_EXT_SVVPTC a runtime one if
RISCV_ALTERNATIVE=n, but it should still be worthwhile to do so given
that TLB flushes are relatively slow.

Signed-off-by: Vivian Wang <wangruikang@...as.ac.cn>
---
 arch/riscv/include/asm/pgtable.h | 15 +++++++--------
 arch/riscv/mm/pgtable.c          | 22 ++++++++++------------
 2 files changed, 17 insertions(+), 20 deletions(-)

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 29e994a9afb6..d1a4bdc36f2c 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -496,8 +496,13 @@ static inline void update_mmu_cache_range(struct vm_fault *vmf,
 		struct vm_area_struct *vma, unsigned long address,
 		pte_t *ptep, unsigned int nr)
 {
-	asm goto(ALTERNATIVE("nop", "j %l[svvptc]", 0, RISCV_ISA_EXT_SVVPTC, 1)
-		 : : : : svvptc);
+	/*
+	 * Svvptc guarantees that the new valid pte will be visible within
+	 * a bounded timeframe, so when the uarch does not cache invalid
+	 * entries, we don't have to do anything.
+	 */
+	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SVVPTC))
+		return;
 
 	/*
 	 * The kernel assumes that TLBs don't cache invalid entries, but
@@ -509,12 +514,6 @@ static inline void update_mmu_cache_range(struct vm_fault *vmf,
 	while (nr--)
 		local_flush_tlb_page(address + nr * PAGE_SIZE);
 
-svvptc:;
-	/*
-	 * Svvptc guarantees that the new valid pte will be visible within
-	 * a bounded timeframe, so when the uarch does not cache invalid
-	 * entries, we don't have to do anything.
-	 */
 }
 #define update_mmu_cache(vma, addr, ptep) \
 	update_mmu_cache_range(NULL, vma, addr, ptep, 1)
diff --git a/arch/riscv/mm/pgtable.c b/arch/riscv/mm/pgtable.c
index 8b6c0a112a8d..807c0a0de182 100644
--- a/arch/riscv/mm/pgtable.c
+++ b/arch/riscv/mm/pgtable.c
@@ -9,8 +9,16 @@ int ptep_set_access_flags(struct vm_area_struct *vma,
 			  unsigned long address, pte_t *ptep,
 			  pte_t entry, int dirty)
 {
-	asm goto(ALTERNATIVE("nop", "j %l[svvptc]", 0, RISCV_ISA_EXT_SVVPTC, 1)
-		 : : : : svvptc);
+	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SVVPTC)) {
+		if (!pte_same(ptep_get(ptep), entry)) {
+			__set_pte_at(vma->vm_mm, ptep, entry);
+			/* Here only not svadu is impacted */
+			flush_tlb_page(vma, address);
+			return true;
+		}
+
+		return false;
+	}
 
 	if (!pte_same(ptep_get(ptep), entry))
 		__set_pte_at(vma->vm_mm, ptep, entry);
@@ -19,16 +27,6 @@ int ptep_set_access_flags(struct vm_area_struct *vma,
 	 * the case that the PTE changed and the spurious fault case.
 	 */
 	return true;
-
-svvptc:
-	if (!pte_same(ptep_get(ptep), entry)) {
-		__set_pte_at(vma->vm_mm, ptep, entry);
-		/* Here only not svadu is impacted */
-		flush_tlb_page(vma, address);
-		return true;
-	}
-
-	return false;
 }
 
 int ptep_test_and_clear_young(struct vm_area_struct *vma,

-- 
2.51.0