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virt: Improve detection of EC2 metal instances

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The current detection code relies on /sys/firmware/dmi/entries/0-0/raw
to disambiguate Amazon EC2 virtualized from metal instances.

Unfortunately this file is root only. Thus on a c6g.metal instance
(aarch64), we observe something like this:

$ systemd-detect-virt
amazon
$ sudo systemd-detect-virt
none

Only the latter is correct.

The right long term fix is to extend the kernel to expose the SMBIOS BIOS
Characteristics properly via /sys/class/dmi, but until this happens (and
for backwards compatibility when it does), we need a plan B.

This change implements such a workaround by falling back to using the
instance type from DMI and looking at the ".metal" string present on
metal instances.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Benjamin Herrenschmidt 2021-09-03 11:36:46 +10:00 committed by Yu Watanabe
parent c116f23394
commit f90eea7d18
1 changed files with 30 additions and 2 deletions
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32
src/basic/virt.c
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@ -235,8 +235,36 @@ static int detect_vm_dmi(void) {
/* The DMI vendor tables in /sys/class/dmi/id don't help us distinguish between Amazon EC2
* virtual machines and bare-metal instances, so we need to look at SMBIOS. */
if (r == VIRTUALIZATION_AMAZON && detect_vm_smbios() == SMBIOS_VM_BIT_UNSET)
return VIRTUALIZATION_NONE;
if (r == VIRTUALIZATION_AMAZON) {
switch (detect_vm_smbios()) {
case SMBIOS_VM_BIT_SET:
return VIRTUALIZATION_AMAZON;
case SMBIOS_VM_BIT_UNSET:
return VIRTUALIZATION_NONE;
case SMBIOS_VM_BIT_UNKNOWN: {
/* The DMI information we are after is only accessible to the root user,
* so we fallback to using the product name which is less restricted
* to distinguish metal systems from virtualized instances */
_cleanup_free_ char *s = NULL;
r = read_full_virtual_file("/sys/class/dmi/id/product_name", &s, NULL);
/* In EC2, virtualized is much more common than metal, so if for some reason
* we fail to read the DMI data, assume we are virtualized. */
if (r < 0) {
log_debug_errno(r, "Can't read /sys/class/dmi/id/product_name,"
" assuming virtualized: %m");
return VIRTUALIZATION_AMAZON;
}
if (endswith(truncate_nl(s), ".metal")) {
log_debug("DMI product name ends with '.metal', assuming no virtualization");
return VIRTUALIZATION_NONE;
} else
return VIRTUALIZATION_AMAZON;
}
default:
assert_not_reached();
}
}
/* If we haven't identified a VM, but the firmware indicates that there is one, indicate as much. We
* have no further information about what it is. */