[Bug 1906516] Re: [RISCV] sfence.vma need to end the translation block

[Thomas Huth]

The QEMU project is currently moving its bug tracking to another system.
For this we need to know which bugs are still valid and which could be
closed already. Thus we are setting the bug state to "Incomplete" now.

If the bug has already been fixed in the latest upstream version of QEMU,
then please close this ticket as "Fix released".

If it is not fixed yet and you think that this bug report here is still
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    https://gitlab.com/qemu-project/qemu/-/issues

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2) If you don't have an account on gitlab.com and don't intend to get
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the state back to "New" or "Confirmed" within the next 60 days (other-
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Thank you and sorry for the inconvenience.


** Tags added: tcg

** Changed in: qemu
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1906516

Title:
  [RISCV] sfence.vma need to end the translation block

Status in QEMU:
  Incomplete

Bug description:
  QEMU emulator version 5.0.0

  sfence.vma will flush the tlb, so after this instruction, the translation 
block should be end. The following code will only work in single step mode:
  ```
  relocate:
   li a0, OFFSET

   la t0, 1f
   add t0, t0, a0
   csrw stvec, t0

          la t0, early_pgtbl
   srl t0, t0, PAGE_SHIFT
   li t1, SATP_SV39
   or t0, t1, t0

          csrw satp, t0
  1:
   sfence.vma
   la t0, trap_s
   csrw stvec, t0
   ret
  ```

  In this code, I want to relocate pc to virtual address with the OFFSET
  prefix. Before writing to satp, pc run at physic address, stvec has
  been set to label 1 with a virtual prefix and virtual address has been
  mapping in early_pgtbl, after writing satp, qemu will throw a page
  fault, and pc will set to virtual address of label 1.

  The problem is that, in this situation, the translation block will not
  end after sfence.vma, and stvec will be set to trap_s,

  ```
  ----------------
  IN:
  Priv: 1; Virt: 0
  0x00000000800000dc:  00a080b3          add             ra,ra,a0
  0x00000000800000e0:  00007297          auipc           t0,28672        # 
0x800070e0
  0x00000000800000e4:  f2028293          addi            t0,t0,-224
  0x00000000800000e8:  00c2d293          srli            t0,t0,12
  0x00000000800000ec:  fff0031b          addiw           t1,zero,-1
  0x00000000800000f0:  03f31313          slli            t1,t1,63
  0x00000000800000f4:  005362b3          or              t0,t1,t0
  0x00000000800000f8:  18029073          csrrw           zero,satp,t0

  ----------------
  IN:
  Priv: 1; Virt: 0
  0x00000000800000fc:  12000073          sfence.vma      zero,zero
  0x0000000080000100:  00000297          auipc           t0,0            # 
0x80000100
  0x0000000080000104:  1c828293          addi            t0,t0,456
  0x0000000080000108:  10529073          csrrw           zero,stvec,t0

  riscv_raise_exception: 12
  riscv_raise_exception: 12
  riscv_raise_exception: 12
  riscv_raise_exception: 12
  ...
  ```

  So, the program will crash, and the program will work in single step mode:
  ```
  ----------------
  IN:
  Priv: 1; Virt: 0
  0x00000000800000f8:  18029073          csrrw           zero,satp,t0

  ----------------
  IN:
  Priv: 1; Virt: 0
  0x00000000800000fc:  12000073          sfence.vma      zero,zero

  riscv_raise_exception: 12
  ----------------
  IN:
  Priv: 1; Virt: 0
  0xffffffff800000fc:  12000073          sfence.vma      zero,zero

  ----------------
  IN:
  Priv: 1; Virt: 0
  0xffffffff80000100:  00000297          auipc           t0,0            # 
0xffffffff80000100

  ```
  The pc will set to label 1, instead of trap_s.

  I try to patch the code in fence.i in trans_rvi.inc.c to sfence.vma:
  ```
      tcg_gen_movi_tl(cpu_pc, ctx->pc_succ_insn);
      exit_tb(ctx);
      ctx->base.is_jmp = DISAS_NORETURN;
  ```
  This codes can help to end the tranlate block, since I'm not a qemu guy, I'm 
not sure if this is a corret method.

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