Re: [Qemu-devel] VFIO NATIVE_ENDIAN regions question

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 09/08/2014 10:00 AM, Alexey Kardashevskiy wrote:
> On 09/08/2014 02:06 AM, Greg Kurz wrote:
>> On Sat,  6 Sep 2014 12:49:47 +1000
>> Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
>>
>>> At the moment VFIO's BARs are NATIVE_ENDIAN. The idea is that since
>>> it does not parse BARs content and just provides transport, it should
>>> not do byte swaps, the guest does it anyway. That worked fine while
>>> the host was big-endian and it does not work when the host is little-endian.
>>> This happens because ./configure defines static macro TARGET_WORDS_BIGENDIAN
>>> for ppc64 and since there is no ppc64le - endianness of host and guest does
>>> not match and stl_p&co swaps bytes as shown below.
>>>
>>> The proposed patch at the end of this mail fixes the issue for VFIO in
>>> any combination of host-guest, BE-LE (need to double check with BE host).
>>> However since I fail to grasp the idea of having statically defined
>>> TARGET_WORDS_BIGENDIAN, I assume I am missing something big here.
>>>
>>> What would the correct fix be here? Thanks!
>>>
>>>
>>>
>>> Breakpoint 9, vfio_bar_read (opaque=0x10de2e98, addr=0x6f4, size=0x4) at /home/alexey/p/qemu/hw/misc/vfio.c:1140
>>> 1140    {
>>> Missing separate debuginfos, use: zypper install glibc-debuginfo-2.19-15.1.ppc64le libgcc_s1-debuginfo-4.8.3+r212056-4.17.ppc64le libglib-2_0-0-debuginfo-2.38.2-5.8.ppc64le libgthread-2_0-0-debu
>>> ginfo-2.38.2-5.8.ppc64le libpcre1-debuginfo-8.33-3.253.ppc64le libpixman-1-0-debuginfo-0.32.6-1.1.ppc64le libstdc++6-debuginfo-4.8.3+r212056-4.17.ppc64le libz1-debuginfo-1.2.8-4.65.ppc64le
>>> (gdb) bt
>>> #0  vfio_bar_read (opaque=0x10de2e98, addr=0x6f4, size=0x4) at /home/alexey/p/qemu/hw/misc/vfio.c:1140
>>> #1  0x00000000100a4bd4 in memory_region_read_accessor (mr=0x10de2ea8, addr=0x6f4, value=0x3fffb77de320, size=0x4, shift=0x0, mask=0xffffffff) at /home/alexey/p/qemu/memory.c:410
>>> #2  0x00000000100a5000 in access_with_adjusted_size (addr=0x6f4, value=0x3fffb77de320, size=0x4, access_size_min=0x1, access_size_max=0x4, access=0x100a4b38 <memory_region_read_accessor>, mr=0x1
>>> 0de2ea8) at /home/alexey/p/qemu/memory.c:475
>>> #3  0x00000000100a84ac in memory_region_dispatch_read1 (mr=0x10de2ea8, addr=0x6f4, size=0x4) at /home/alexey/p/qemu/memory.c:1097
>>> #4  0x00000000100a85d8 in memory_region_dispatch_read (mr=0x10de2ea8, addr=0x6f4, pval=0x3fffb77de458, size=0x4) at /home/alexey/p/qemu/memory.c:1119
>>> #5  0x00000000100ace24 in io_mem_read (mr=0x10de2ea8, addr=0x6f4, pval=0x3fffb77de458, size=0x4) at /home/alexey/p/qemu/memory.c:1967
>>> #6  0x0000000010013bf8 in address_space_rw (as=0x1081d410 <address_space_memory>, addr=0x1a0b00006f4, buf=0x3fffb7f80028 "", len=0x4, is_write=0x0) at /home/alexey/p/qemu/exec.c:2076
>>> #7  0x0000000010013fa4 in cpu_physical_memory_rw (addr=0x1a0b00006f4, buf=0x3fffb7f80028 "", len=0x4, is_write=0x0) at /home/alexey/p/qemu/exec.c:2121
>>> #8  0x00000000100a015c in kvm_cpu_exec (cpu=0x3fffb77e0010) at /home/alexey/p/qemu/kvm-all.c:1770
>>> #9  0x000000001007ab18 in qemu_kvm_cpu_thread_fn (arg=0x3fffb77e0010) at /home/alexey/p/qemu/cpus.c:940
>>> #10 0x00003fffb7828a64 in start_thread () from /lib64/libpthread.so.0
>>> #11 0x00003fffb7993b00 in clone () from /lib64/libc.so.6
>>> (gdb) n
>>> 1141        VFIOBAR *bar = opaque;
>>> (gdb)
>>> 1148        uint64_t data = 0;
>>> (gdb)
>>> 1150        if (pread(bar->fd, &buf, size, bar->fd_offset + addr) != size) {
>>> (gdb)
>>> 1156        switch (size) {
>>> (gdb)
>>> 1164            data = buf.dword;
>>> (gdb)
>>> 1165            break;
>>> (gdb)
>>> 1171        if (addr == 0x6f4) {
>>> (gdb)
>>> 1172            printf("%s %u size=%d val=%lx\n", __func__, __LINE__, size, data);
>>> (gdb)
>>> vfio_bar_read 1172 size=4 val=4
>>> 1187        vfio_eoi(container_of(bar, VFIODevice, bars[bar->nr]));
>>> (gdb)
>>> 1189        return data;
>>> (gdb)
>>> 1190    }
>>> (gdb)
>>> memory_region_read_accessor (mr=0x10de2ea8, addr=0x6f4, value=0x3fffb77de320, size=0x4, shift=0x0, mask=0xffffffff) at /home/alexey/p/qemu/memory.c:411
>>> 411         trace_memory_region_ops_read(mr, addr, tmp, size);
>>> (gdb)
>>> 412         *value |= (tmp & mask) << shift;
>>> (gdb)
>>> 413     }
>>> (gdb)
>>> access_with_adjusted_size (addr=0x6f4, value=0x3fffb77de320, size=0x4, access_size_min=0x1, access_size_max=0x4, access=0x100a4b38 <memory_region_read_accessor>, mr=0x10de2ea8) at /home/alexey/p
>>> /qemu/memory.c:474
>>> 474             for (i = 0; i < size; i += access_size) {
>>> (gdb)
>>> 483     }
>>> (gdb)
>>> memory_region_dispatch_read1 (mr=0x10de2ea8, addr=0x6f4, size=0x4) at /home/alexey/p/qemu/memory.c:1106
>>> 1106        return data;
>>> (gdb)
>>> 1107    }
>>> (gdb)
>>> memory_region_dispatch_read (mr=0x10de2ea8, addr=0x6f4, pval=0x3fffb77de458, size=0x4) at /home/alexey/p/qemu/memory.c:1120
>>> 1120        adjust_endianness(mr, pval, size);
>>> (gdb) s
>>> adjust_endianness (mr=0x10de2ea8, data=0x3fffb77de458, size=0x4) at /home/alexey/p/qemu/memory.c:364
>>> 364     {
>>> (gdb) n
>>> 365         if (memory_region_wrong_endianness(mr)) {
>>> (gdb)
>>> 382     }
>>> (gdb)
>>> memory_region_dispatch_read (mr=0x10de2ea8, addr=0x6f4, pval=0x3fffb77de458, size=0x4) at /home/alexey/p/qemu/memory.c:1121
>>> 1121        return false;
>>> (gdb)
>>> 1122    }
>>> (gdb)
>>> io_mem_read (mr=0x10de2ea8, addr=0x6f4, pval=0x3fffb77de458, size=0x4) at /home/alexey/p/qemu/memory.c:1968
>>> 1968    }
>>> (gdb)
>>> address_space_rw (as=0x1081d410 <address_space_memory>, addr=0x1a0b00006f4, buf=0x3fffb7f80028 "", len=0x4, is_write=0x0) at /home/alexey/p/qemu/exec.c:2077
>>> 2077                        stl_p(buf, val);
>>> (gdb) s
>>> stl_be_p (ptr=0x3fffb7f80028, v=0x4) at /home/alexey/p/qemu/include/qemu/bswap.h:377
>>> 377     {
>>> (gdb) n
>>>
>>> ---
>>>  include/exec/cpu-all.h | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
>>> index f9d132f..f3a761a 100644
>>> --- a/include/exec/cpu-all.h
>>> +++ b/include/exec/cpu-all.h
>>> @@ -152,7 +152,7 @@ static inline void tswap64s(uint64_t *s)
>>>   */
>>>
>>>  /* target-endianness CPU memory access functions */
>>> -#if defined(TARGET_WORDS_BIGENDIAN)
>>> +#if defined(HOST_WORDS_BIGENDIAN)
>>
>> AFAIK these accessors implement target CPU accesses to memory... I
>> don't see why they should be affected by the host endianness.
>> If you have an endianness issue related to HOST_WORDS_BIGENDIAN,
>> my guess is that you need to cancel the byteswap in hw/misc/vfio.c.
> 
> 
> That is exactly the problem - swaps are cancelled already, VFIO is native
> endian now.


Aaaand this is not memory, this is MMIO:


int kvm_cpu_exec(CPUState *cpu)
{
[...]
 case KVM_EXIT_MMIO:
     DPRINTF("handle_mmio\n");
     cpu_physical_memory_rw(run->mmio.phys_addr,
                            run->mmio.data,
                            run->mmio.len,
                            run->mmio.is_write);
     ret = 0;
     break;



> 
> 
>>
>>>  #define lduw_p(p) lduw_be_p(p)
>>>  #define ldsw_p(p) ldsw_be_p(p)
>>>  #define ldl_p(p) ldl_be_p(p)
>>
> 
> 


-- 
Alexey