tests: shrink sv39 PMEM size and add sfence.vma

shrink PMEM size to reduce test setup time
add sfence.vma before accessing any newly mapped virtual addresses

am/src/nemu/isa/riscv/vme.c

@@ -20,7 +20,7 @@ static const _Area segments[] = {      // Kernel memory mappings
   RANGE_LEN(0x3c000000, 0x4000000), // PLIC
   RANGE_LEN(0xc0000000, 0x100000),  // page table test allocates from this position
 #elif defined(__ARCH_RISCV64_XS_SOUTHLAKE) || defined(__ARCH_RISCV64_XS_SOUTHLAKE_FLASH)
-  RANGE_LEN(0x2000000000, 0x8000000), // PMEM
+  RANGE_LEN(0x2000000000, 0x800000), // PMEM
   RANGE_LEN(0x1f00050000, 0x1000),    // uart
   // RANGE_LEN(CLINT_MMIO, 0x10000),     // clint/timer
   // RANGE_LEN(0x1f0c000000, 0x4000000), // PLIC

tests/amtest/src/tests/sv39.c

@@ -86,7 +86,7 @@ void sv39_test() {
 #endif
   irq_handler_reg(EXCEPTION_STORE_PAGE_FAULT, &store_page_fault_handler);
   irq_handler_reg(EXCEPTION_LOAD_PAGE_FAULT, &load_page_fault_handler);
-
+  asm volatile("sfence.vma");
   printf("test sv39 data write\n");
   *w_ptr = 'a';