[Xen-devel] Problem with IOMEM and domain reboot

[Oleksandr Andrushchenko <andr2000@xxxxxxxxx>]

Hi, all!

While trying to reboot a domain which has iomem configured
(we are passing through some devices), I found an issue,
that after domain reboot those iomem's are incorrectly re-mapped,
e.g. for the configuration snippet below fe960 -> 0.

Part of the domain config I use:
iomem=[
    "0xfd010,1@0xfd000",
    "fe960,8",
]

During domain creation:
libxl_create.c:210:libxl__domain_build_info_setdefault: iomem gfn fd000 
start fd010
libxl_create.c:210:libxl__domain_build_info_setdefault: iomem gfn 
ffffffffffffffff start fe960
which means that for fe960 initial value was set to LIBXL_INVALID_GFN
and then on domain configuration, 
tools/libxl/libxl_create.c:libxl__domain_build_info_setdefault:
    for (i = 0 ; i < b_info->num_iomem; i++)
        if (b_info->iomem[i].gfn == LIBXL_INVALID_GFN)
            b_info->iomem[i].gfn = b_info->iomem[i].start;

made that GFN for fe960 to be set to the correct value.

But during domain reboot I see that 
tools/xl/xl_vmcontrol.c:reload_domain_config
tries to replicate configuration from the original domain config
being rebooted, but that leads to iomem's GFN to be set to 0 (if configured
in form [IOMEM_START,NUM_PAGES], but for [IOMEM_START,NUM_PAGES[@GFN] it 
is ok):
iomem gfn fd000 start fd010
iomem gfn 0 start fe960

Thus, further domain restart procedure leads to invalid mapping, e.g. 
fe960 -> 0.
I created a patch which allowed me to reboot the domain, but I would love
to hear comments on what would be the proper fix.

Thank you,
Oleksandr

Attachment: 0001-HACK-Reset-iomem-s-gfn-to-LIBXL_INVALID_GFN-on-reboo.patch
Description: Text Data

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