Bogon kernel command line options: Difference between revisions
Created page with "'''dankblog! 2022-03-12, 1842 EDT, at the danktower''' i was looking at my dmesg output today, wanting to know something about IOMMU, and noticed the following line: <tt>[ 0.015134] Unknown kernel command line parameters "BOOT_IMAGE=/boot/vmlinuz-5.16.13nlb2 mem_encrypt=off intel_iommu=on", will be passed to user space </tt> first off, some basic [https://man7.org/linux/man-pages/man7/kernel-command-line.7.html kernel command line] fa..." |
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<li>hyphens and underscores are equivalent</li> | <li>hyphens and underscores are equivalent</li> | ||
</ul> | </ul> | ||
but unrecognized items get this informational line. let's take a look at them: | |||
<ul> | |||
<li><tt>BOOT_IMAGE=/boot/vmlinuz-5.16.13nlb2</tt> this is set by grub since grub 1.91, released 2005-10-15. i'm not sure why, or who consumes it. LILO set this parameter as well, and this might have just been a compatibility thing, so it might be lost in the river of time.</li> | |||
<li><tt>mem_encrypt=off</tt> this refers to AMD's [https://en.wikichip.org/wiki/x86/sme Secure Memory Encryption] extension, allowing per-page transparent encryption. i've got this disabled in my kernel config now (<tt>CONFIG_AMD_MEM_ENCRYPT</tt>), so it's no longer recognized. i've removed it.</li> | |||
<li><tt>intel_iommu=on</tt> well duh i don't have an intel in this machine. i want <tt>iommu=pt iommu=1</tt></li> | |||
</ul> | |||
the rest of my command line appears to be valid (inspected at <tt>/proc/cmdline</tt>): | |||
<tt>BOOT_IMAGE=/boot/vmlinuz-5.16.13nlb2 root=UUID=939be09a-b63d-403c-996a-8b9866313fbb ro mem_encrypt=off psi=0 acpi_enforce_resources=lax intel_iommu=on</tt> | |||
<tt>psi=0</tt> refers to the Pressure Stall Information feedback system introduced in 2018 by Facebook hackers, which you can read about [https://www.kernel.org/doc/html/latest/accounting/psi.html here] or [https://lwn.net/Articles/764761/ here]. | |||
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