Re: [Qemu-devel] VFIO NATIVE_ENDIAN regions question

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 09/08/2014 10:04 PM, Alexander Graf wrote:
> 
> 
> On 08.09.14 02:06, Alexey Kardashevskiy wrote:
>> On 09/08/2014 06:35 AM, Alexander Graf wrote:
>>>
>>>
>>> On 06.09.14 04:49, Alexey Kardashevskiy 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);
>>>
>>> How do you end up in stl_p on an mmio read? That sounds odd.
>>
>> Sorry, I am not following you here. What would not be odd here? It is
>> emulated mmio, stl_p() stores to run->mmio.data.
> 
> Ok, I'm slowly starting to grasp the problem. Can you please try the
> following patch?


This or I simply revert "Make BARs native endian" and fix ROM BAR.

commit c40708176a6b52b73bec14796b7c71b882ceb102
Author:     Alexey Kardashevskiy <aik@ozlabs.ru>
AuthorDate: Mon Jun 30 09:52:58 2014 -0600
Commit:     Alex Williamson <alex.williamson@redhat.com>
CommitDate: Mon Jun 30 09:52:58 2014 -0600
    vfio: Make BARs native endian



> 
> Alex
> 
> diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c
> index 40dcaa6..6283636 100644
> --- a/hw/misc/vfio.c
> +++ b/hw/misc/vfio.c
> @@ -1095,13 +1095,13 @@ static void vfio_bar_write(void *opaque, hwaddr
> addr,
> 
>      switch (size) {
>      case 1:
> -        buf.byte = data;
> +        stb_p(&buf.byte, data);
>          break;
>      case 2:
> -        buf.word = data;
> +        stw_le_p(&buf.word, data);
>          break;
>      case 4:
> -        buf.dword = data;
> +        stl_le_p(&buf.dword, data);
>          break;
>      default:
>          hw_error("vfio: unsupported write size, %d bytes", size);
> @@ -1155,13 +1155,13 @@ static uint64_t vfio_bar_read(void *opaque,
> 
>      switch (size) {
>      case 1:
> -        data = buf.byte;
> +        data = ldub_p(&buf.byte);
>          break;
>      case 2:
> -        data = buf.word;
> +        data = lduw_le_p(&buf.word);
>          break;
>      case 4:
> -        data = buf.dword;
> +        data = ldl_le_p(&buf.dword);
>          break;
>      default:
>          hw_error("vfio: unsupported read size, %d bytes", size);
> @@ -1188,7 +1188,7 @@ static uint64_t vfio_bar_read(void *opaque,
>  static const MemoryRegionOps vfio_bar_ops = {
>      .read = vfio_bar_read,
>      .write = vfio_bar_write,
> -    .endianness = DEVICE_NATIVE_ENDIAN,
> +    .endianness = DEVICE_LITTLE_ENDIAN,
>  };
> 
>  static void vfio_pci_load_rom(VFIODevice *vdev)
> 


-- 
Alexey