Re: [Qemu-devel] qemu softmmu inlined lookup sequence

[Xin Tong]

On Mon, Apr 16, 2012 at 10:51 PM, 陳韋任 <address@hidden> wrote:
>> what does the inline sequence look like ? what kind of things (other
>> than refill tlb) performed in callout but not the inlined sequence ?
>
>  What do you mean by the inline sequence, the host binary? If so,
>
> ---
>  ---- 0xe86c8
>  mov_i32 tmp2,edi
>  qemu_ld8u tmp0,tmp2,$0x0
>  ext8u_i32 tmp12,tmp0
>  movi_i32 tmp13,$0xffffff00
>  and_i32 edx,edx,tmp13
>  or_i32 edx,edx,tmp12
>
> OUT: [size=172]
> 0x40000ce0:  mov    0x1c(%r14),%ebp
> 0x40000ce4:  mov    %ebp,%esi               <--- (a)
> 0x40000ce6:  mov    %ebp,%edi
> 0x40000ce8:  shr    $0x7,%esi
> 0x40000ceb:  and    $0xfffff000,%edi
> 0x40000cf1:  and    $0x1fe0,%esi
> 0x40000cf7:  lea    0x348(%r14,%rsi,1),%rsi
> 0x40000cff:  cmp    (%rsi),%edi
> 0x40000d01:  mov    %ebp,%edi
> 0x40000d03:  jne    0x40000d0e
> 0x40000d05:  add    0x10(%rsi),%rdi
> 0x40000d09:  movzbl (%rdi),%ebp
> 0x40000d0c:  jmp    0x40000d18
> 0x40000d0e:  xor    %esi,%esi
> 0x40000d10:  callq  0x54cf8e                <--- (b)
> 0x40000d15:  movzbl %al,%ebp
> 0x40000d18:  movzbl %bpl,%ebp
> 0x40000d1c:  mov    0x8(%r14),%ebx
> ---
>


I had anotated the inlined TLB lookup sequence. can you please help me
verify whether it is correct ? I am putting this in a paper... must
make sure it is correct ...


# %ebp is the guest virtual address.
0x40000ce4:  mov    %ebp,%esi
# %ebp is the guest virtual address.
0x40000ce6:  mov    %ebp,%edi

# take the page address of the guest virtual address.
# take the bit 12 - 19 of the guest virtual address.
0x40000ce8:  shr    $0x7,%esi
0x40000ceb:  and    $0xfffff000,%edi
0x40000cf1:  and    $0x1fe0,%esi

# index into the software tlb using the bit 12 - 19.
0x40000cf7:  lea    0x348(%r14,%rsi,1),%rsi

# check for a possible match
0x40000cff:  cmp    (%rsi),%edi

0x40000d01:  mov    %ebp,%edi
0x40000d03:  jne    0x40000d0e

# there is a match, calculate the translated address.
0x40000d05:  add    0x10(%rsi),%rdi
0x40000d09:  movzbl (%rdi),%ebp
0x40000d0c:  jmp    0x40000d18

# can not find a match, perform the callout.
0x40000d0e:  xor    %esi,%esi
0x40000d10:  callq  callout_TLBLookup

# other emulation code
0x40000d18:  movzbl %bpl,%ebp
0x40000d1c:  mov    0x8(%r14),%ebx


>  The code between (a) and (b) is (almost) what TLB lookup hit/miss looks like.
> If TLB miss, it will call something like __ldb_mmu (b). __ldb_mmu will try to
> walk guest page table, then fill TLB entry if page table hit, or raise a guest
> page fault exception if page table miss.
>
> HTH,
> chenwj
>
> --
> Wei-Ren Chen (陳韋任)
> Computer Systems Lab, Institute of Information Science,
> Academia Sinica, Taiwan (R.O.C.)
> Tel:886-2-2788-3799 #1667
> Homepage: http://people.cs.nctu.edu.tw/~chenwj