Revert "riscv: mm: notify remote harts about mmu cache updates"

This reverts the remaining bits of commit 4bd1d80 ("riscv: mm:
notify remote harts harts about mmu cache updates").

According to bug reports, suggested approach to fix stale TLB entries
is not sufficient. It needs to be replaced by a more robust solution.

Fixes: 4bd1d80 ("riscv: mm: notify remote harts about mmu cache updates")
Reported-by: Zong Li <[email protected]>
Reported-by: Lad Prabhakar <[email protected]>
Signed-off-by: Sergey Matyukevich <[email protected]>
Cc: [email protected]
Reviewed-by: Guo Ren <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: sm-sc

arch/riscv/include/asm/mmu.h

@@ -19,8 +19,6 @@ typedef struct {
 #ifdef CONFIG_SMP
 	/* A local icache flush is needed before user execution can resume. */
 	cpumask_t icache_stale_mask;
-	/* A local tlb flush is needed before user execution can resume. */
-	cpumask_t tlb_stale_mask;
 #endif
 } mm_context_t;
 

arch/riscv/include/asm/tlbflush.h

@@ -22,24 +22,6 @@ static inline void local_flush_tlb_page(unsigned long addr)
 {
 	ALT_FLUSH_TLB_PAGE(__asm__ __volatile__ ("sfence.vma %0" : : "r" (addr) : "memory"));
 }
-
-static inline void local_flush_tlb_all_asid(unsigned long asid)
-{
-	__asm__ __volatile__ ("sfence.vma x0, %0"
-			:
-			: "r" (asid)
-			: "memory");
-}
-
-static inline void local_flush_tlb_page_asid(unsigned long addr,
-		unsigned long asid)
-{
-	__asm__ __volatile__ ("sfence.vma %0, %1"
-			:
-			: "r" (addr), "r" (asid)
-			: "memory");
-}
-
 #else /* CONFIG_MMU */
 #define local_flush_tlb_all()			do { } while (0)
 #define local_flush_tlb_page(addr)		do { } while (0)

arch/riscv/mm/context.c

@@ -196,16 +196,6 @@ static void set_mm_asid(struct mm_struct *mm, unsigned int cpu)
 
 	if (need_flush_tlb)
 		local_flush_tlb_all();
-#ifdef CONFIG_SMP
-	else {
-		cpumask_t *mask = &mm->context.tlb_stale_mask;
-
-		if (cpumask_test_cpu(cpu, mask)) {
-			cpumask_clear_cpu(cpu, mask);
-			local_flush_tlb_all_asid(cntx & asid_mask);
-		}
-	}
-#endif
 }
 
 static void set_mm_noasid(struct mm_struct *mm)

arch/riscv/mm/tlbflush.c

@@ -5,7 +5,23 @@
 #include <linux/sched.h>
 #include <asm/sbi.h>
 #include <asm/mmu_context.h>
-#include <asm/tlbflush.h>
+
+static inline void local_flush_tlb_all_asid(unsigned long asid)
+{
+	__asm__ __volatile__ ("sfence.vma x0, %0"
+			:
+			: "r" (asid)
+			: "memory");
+}
+
+static inline void local_flush_tlb_page_asid(unsigned long addr,
+		unsigned long asid)
+{
+	__asm__ __volatile__ ("sfence.vma %0, %1"
+			:
+			: "r" (addr), "r" (asid)
+			: "memory");
+}
 
 void flush_tlb_all(void)
 {
@@ -15,7 +31,6 @@ void flush_tlb_all(void)
 static void __sbi_tlb_flush_range(struct mm_struct *mm, unsigned long start,
 				  unsigned long size, unsigned long stride)
 {
-	struct cpumask *pmask = &mm->context.tlb_stale_mask;
 	struct cpumask *cmask = mm_cpumask(mm);
 	unsigned int cpuid;
 	bool broadcast;
@@ -29,15 +44,6 @@ static void __sbi_tlb_flush_range(struct mm_struct *mm, unsigned long start,
 	if (static_branch_unlikely(&use_asid_allocator)) {
 		unsigned long asid = atomic_long_read(&mm->context.id);
 
-		/*
-		 * TLB will be immediately flushed on harts concurrently
-		 * executing this MM context. TLB flush on other harts
-		 * is deferred until this MM context migrates there.
-		 */
-		cpumask_setall(pmask);
-		cpumask_clear_cpu(cpuid, pmask);
-		cpumask_andnot(pmask, pmask, cmask);
-
 		if (broadcast) {
 			sbi_remote_sfence_vma_asid(cmask, start, size, asid);
 		} else if (size <= stride) {