Am Mon, 13 Jan 2020 11:36:27 +0100 schrieb Olaf Hering <o...@aepfle.de>:
> This HVM domU fails to live migrate from staging-4.12 to staging-4.13:
It turned out libxl does not configure qemu correctly at runtime:
libxl__build_device_model_args_new() uses 'qemu -machine xenfv', perhaps with
the assumption that 'xenfv' does the right thing. Unfortunately, 'xenfv'
entirely ignores compatibility of "pc-i440fx" between qemu versions, 'xenfv'
just maps to 'pc' aka 'the lastest'. Instead of 'qemu -machine xenfv', libxl
should run 'qemu -machine pc-i440fx-3.0 -device xen-platform -accel xen' to
make sure the domU can be migrated safely to future versions of qemu.
Maybe there should also be a way to select a specific variant of "pc-i440fx".
Currently the only way to do that is to use device_model_args_hvm= in xl.cfg.
Unfortunately libvirt does not support "b_info->extra*".
Should the string "pc-i440fx-3.0" become a configure option?
I think this (untested) patch has to be applied to staging-4.13:
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -1715,23 +1715,20 @@ static int libxl__build_device_model_args_new(libxl__gc
*gc,
for (i = 0; b_info->extra && b_info->extra[i] != NULL; i++)
flexarray_append(dm_args, b_info->extra[i]);
- flexarray_append(dm_args, "-machine");
switch (b_info->type) {
case LIBXL_DOMAIN_TYPE_PVH:
case LIBXL_DOMAIN_TYPE_PV:
+ flexarray_append(dm_args, "-machine");
flexarray_append(dm_args, "xenpv");
for (i = 0; b_info->extra_pv && b_info->extra_pv[i] != NULL; i++)
flexarray_append(dm_args, b_info->extra_pv[i]);
break;
case LIBXL_DOMAIN_TYPE_HVM:
- if (!libxl_defbool_val(b_info->u.hvm.xen_platform_pci)) {
- /* Switching here to the machine "pc" which does not add
- * the xen-platform device instead of the default "xenfv" machine.
- */
- machinearg = libxl__strdup(gc, "pc,accel=xen");
- } else {
- machinearg = libxl__strdup(gc, "xenfv");
+ if (libxl_defbool_val(b_info->u.hvm.xen_platform_pci)) {
+ flexarray_append(dm_args, "-device");
+ flexarray_append(dm_args, "xen-platform");
}
+ machinearg = libxl__strdup(gc, "pc-i440fx-3.0,accel=xen");
if (b_info->u.hvm.mmio_hole_memkb) {
uint64_t max_ram_below_4g = (1ULL << 32) -
(b_info->u.hvm.mmio_hole_memkb << 10);
@@ -1762,6 +1759,7 @@ static int libxl__build_device_model_args_new(libxl__gc
*gc,
}
}
+ flexarray_append(dm_args, "-machine");
flexarray_append(dm_args, machinearg);
for (i = 0; b_info->extra_hvm && b_info->extra_hvm[i] != NULL; i++)
flexarray_append(dm_args, b_info->extra_hvm[i]);
Olaf
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