[PATCH 1/1] riscv: Implement arch_sync_kernel_mappings() for "preventive" TLB flush

[Dylan Jhong]

Since RISC-V is a microarchitecture that allows caching invalid entries in the TLB,
it is necessary to issue a "preventive" SFENCE.VMA to ensure that each core obtains
the correct kernel mapping.

The patch implements TLB flushing in arch_sync_kernel_mappings(), ensuring that kernel
page table mappings created via vmap/vmalloc() are updated before switching MM.

Signed-off-by: Dylan Jhong <dylan at andestech.com>
---
 arch/riscv/include/asm/page.h |  2 ++
 arch/riscv/mm/tlbflush.c      | 12 ++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
index b55ba20903ec..6c86ab69687e 100644
--- a/arch/riscv/include/asm/page.h
+++ b/arch/riscv/include/asm/page.h
@@ -21,6 +21,8 @@
 #define HPAGE_MASK              (~(HPAGE_SIZE - 1))
 #define HUGETLB_PAGE_ORDER      (HPAGE_SHIFT - PAGE_SHIFT)
 
+#define ARCH_PAGE_TABLE_SYNC_MASK	PGTBL_PTE_MODIFIED
+
 /*
  * PAGE_OFFSET -- the first address of the first page of memory.
  * When not using MMU this corresponds to the first free page in
diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 77be59aadc73..d63364948c85 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -149,3 +149,15 @@ void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
 	__flush_tlb_range(vma->vm_mm, start, end - start, PMD_SIZE);
 }
 #endif
+
+/*
+ * Since RISC-V is a microarchitecture that allows caching invalid entries in the TLB,
+ * it is necessary to issue a "preventive" SFENCE.VMA to ensure that each core obtains
+ * the correct kernel mapping. arch_sync_kernel_mappings() will ensure that kernel
+ * page table mappings created via vmap/vmalloc() are updated before switching MM.
+ */
+void arch_sync_kernel_mappings(unsigned long start, unsigned long end)
+{
+	if (start < VMALLOC_END && end > VMALLOC_START)
+		flush_tlb_all();
+}
\ No newline at end of file
-- 
2.34.1