[PATCH] Insert SFENCE.VMA in function set_pte_at for RISCV

[Jiuyang Liu <liu@jiuyang.me>]

This patch inserts SFENCE.VMA after modifying PTE based on RISC-V
specification.

arch/riscv/include/asm/pgtable.h:
1. implement pte_user, pte_global and pte_leaf to check correspond
attribute of a pte_t.

2. insert SFENCE.VMA in set_pte_at based on RISC-V Volume 2, Privileged
Spec v. 20190608 page 66 and 67:
If software modifies a non-leaf PTE, it should execute SFENCE.VMA with
rs1=x0. If any PTE along the traversal path had its G bit set, rs2 must
be x0; otherwise, rs2 should be set to the ASID for which the
translation is being modified.
If software modifies a leaf PTE, it should execute SFENCE.VMA with rs1
set to a virtual address within the page. If any PTE along the traversal
path had its G bit set, rs2 must be x0; otherwise, rs2 should be set to
the ASID for which the translation is being modified.

arch/riscv/include/asm/tlbflush.h:
1. implement get_current_asid to get current program asid.
2. implement local_flush_tlb_asid to flush tlb with asid.

Signed-off-by: Jiuyang Liu <liu@jiuyang.me>
---
 arch/riscv/include/asm/pgtable.h  | 27 +++++++++++++++++++++++++++
 arch/riscv/include/asm/tlbflush.h | 12 ++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index ebf817c1bdf4..5a47c60372c1 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -222,6 +222,16 @@ static inline int pte_write(pte_t pte)
 	return pte_val(pte) & _PAGE_WRITE;
 }
 
+static inline int pte_user(pte_t pte)
+{
+	return pte_val(pte) & _PAGE_USER;
+}
+
+static inline int pte_global(pte_t pte)
+{
+	return pte_val(pte) & _PAGE_GLOBAL;
+}
+
 static inline int pte_exec(pte_t pte)
 {
 	return pte_val(pte) & _PAGE_EXEC;
@@ -248,6 +258,11 @@ static inline int pte_special(pte_t pte)
 	return pte_val(pte) & _PAGE_SPECIAL;
 }
 
+static inline int pte_leaf(pte_t pte)
+{
+	return pte_val(pte) & (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC);
+}
+
 /* static inline pte_t pte_rdprotect(pte_t pte) */
 
 static inline pte_t pte_wrprotect(pte_t pte)
@@ -358,6 +373,18 @@ static inline void set_pte_at(struct mm_struct *mm,
 		flush_icache_pte(pteval);
 
 	set_pte(ptep, pteval);
+
+	if (pte_present(pteval)) {
+		if (pte_leaf(pteval)) {
+			local_flush_tlb_page(addr);
+		} else {
+			if (pte_global(pteval))
+				local_flush_tlb_all();
+			else
+				local_flush_tlb_asid();
+
+		}
+	}
 }
 
 static inline void pte_clear(struct mm_struct *mm,
diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index 394cfbccdcd9..1f9b62b3670b 100644
--- a/arch/riscv/include/asm/tlbflush.h
+++ b/arch/riscv/include/asm/tlbflush.h
@@ -21,6 +21,18 @@ static inline void local_flush_tlb_page(unsigned long addr)
 {
 	__asm__ __volatile__ ("sfence.vma %0" : : "r" (addr) : "memory");
 }
+
+static inline unsigned long get_current_asid(void)
+{
+	return (csr_read(CSR_SATP) >> SATP_ASID_SHIFT) & SATP_ASID_MASK;
+}
+
+static inline void local_flush_tlb_asid(void)
+{
+	unsigned long asid = get_current_asid();
+	__asm__ __volatile__ ("sfence.vma x0, %0" : : "r" (asid) : "memory");
+}
+
 #else /* CONFIG_MMU */
 #define local_flush_tlb_all()			do { } while (0)
 #define local_flush_tlb_page(addr)		do { } while (0)
-- 
2.30.2