Investigate exposing coreboot tables through sysfs for x86 (so kexec to xen can expose them to dom0 for cbmem)

[tlaurion]

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@krystian-hebel said:

I've added exposing CBMEM (i.e. memory region) as sysfs files for PPC64 in https://github.com/linuxboot/heads/blob/master/patches/linux-5.5-openpower/0011-drivers-firmware-google-expose-CBMEM-as-sysfs-file.patch, it may work on x86 after CBMEM is added as a resource to ACPI table on coreboot side. IIUC Xen passes ACPI to dom0, and the full coreboot tables are mapped there, so in theory this should work