fix(xen): exclude 1MB lowmem from e820 scaling - #22
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Fixes: b0a3e48 ("x86/dom0: distribute PVH dom0 E820 RAM proportionally across host regions")
bleggett
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kaniini
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Aug 10, 2026
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Fixes: b0a3e48 ("x86/dom0: distribute PVH dom0 E820 RAM proportionally across host regions")
Fixup to Edera-local b0a3e48: the PVH dom0 E820 proportional trim rationed the sub-1MB slice along with everything else, which at certain scaling sizes would break Linux's real-mode trampoline, which needs memory under 1 MB whose size doesn't scale with dom0's share.
A small dom0 on a large host got 12-80 KB where it needed a page-aligned chunk, and so died in
init_real_mode()before having a console.I was able to repro the dom0 crash locally with our 4.21 and
dom0_mem=1G+35%,max:8G, and this fix resolves it, allowing successful boot again.Also needs a 4.22 port, which I'll do separately. Targeting 4.21 first since we need to get a hotfix out on an existing release.