[Xen-devel] Some Xen pci-passthrough questions

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Hi Boris / Andrew,

In the aftermath of the linux mmap path I have some questions regarding 
pci-passthrough:

- Is pci-passthrough in combination with an auto-ballooning dom0 supposed to be 
a supported combination ?

    I have used dom0_maxmem settings for dom0 since ages and that works fine 
and stable, 
    but while doing some testing around the linux mmap patch i also thought to 
try an auto-ballooning dom0.

    That ended up in a crashing PV guest with pci-passthrough and a strange 
error on two HVM's with pci-passthrough,
    about vcpu's (while no configurations where changed).

    So if it is supported i probably have some more testing and reporting to do 
...


- While adding some extra logging and enabling the logging on xen pt in qemu,
  i wonder if it wouldn't be beneficial to have at least some basic logging 
permanently enabled ? 

- Enabling the xen pt logging in qemu spit out some things, i wonder if they 
are normal:

        qemu-system-i386: -serial pty: char device redirected to /dev/pts/16 
(label serial0)
        [00:05.0] xen_pt_realize: Assigning real physical device 08:00.0 to 
devfn 0x28
        [00:05.0] xen_pt_register_regions: IO region 0 registered 
(size=0x00002000 base_addr=0xfe1fe000 type: 0x4)

    Are these somehow expected / benign (they also occur when pci passthrough 
is succesful) ?:
        [00:05.0] xen_pt_config_reg_init: Offset 0x000e mismatch! 
Emulated=0x0080, host=0x0000, syncing to 0x0080.
        [00:05.0] xen_pt_config_reg_init: Offset 0x0010 mismatch! 
Emulated=0x0000, host=0xfe1fe004, syncing to 0xfe1fe004.
        [00:05.0] xen_pt_config_reg_init: Offset 0x0052 mismatch! 
Emulated=0x0000, host=0x4803, syncing to 0x0003.
        [00:05.0] xen_pt_config_reg_init: Offset 0x0072 mismatch! 
Emulated=0x0000, host=0x0086, syncing to 0x0080.
        [00:05.0] xen_pt_config_reg_init: Offset 0x00a4 mismatch! 
Emulated=0x0000, host=0x8fc0, syncing to 0x8fc0.
        [00:05.0] xen_pt_config_reg_init: Offset 0x00b2 mismatch! 
Emulated=0x0000, host=0x1012, syncing to 0x1012.

        [00:05.0] xen_pt_msix_init: get MSI-X table BAR base 0xfe1fe000
        [00:05.0] xen_pt_msix_init: table_off = 0x1000, total_entries = 8
        [00:05.0] xen_pt_msix_init: table_off = 0x1000, total_entries = 8, 
PCI_MSIX_ENTRY_SIZE = 0x10,  msix->table_offset_adjust = 0,  msix->table_base = 
0xfe1fe000
        [00:05.0] xen_pt_msix_init: Error: Can't map physical MSI-X table: 
Invalid argument
        [00:05.0] xen_pt_msix_size_init: Error: Internal error: Invalid 
xen_pt_msix_init.
        Failed to initialize 12/15, type = 0x1, rc: -22
        [00:05.0] xen_pt_msi_set_enable: disabling MSI.

    This crash seems to indicate the above disabling of MSI isn't handled well 
enough to prevent this from happening: 
        *** Error in `/usr/local/lib/xen/bin/qemu-system-i386': corrupted size 
vs. prev_size: 0x000055ce13565570 ***
        ======= Backtrace: =========
        /lib/x86_64-linux-gnu/libc.so.6(+0x70bcb)[0x7f700ab7ebcb]
        /lib/x86_64-linux-gnu/libc.so.6(+0x76f96)[0x7f700ab84f96]
        <snip>

--
Sander

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