https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=231760
John Baldwin <j...@freebsd.org> changed:
What |Removed |Added
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CC| |ma...@freebsd.org
--- Comment #16 from John Baldwin <j...@freebsd.org> ---
I got access to two laptops at BSDCan tonight and figured out the bug. I'll
clean up the patch I came up with and post it soonish. However, the short
version is that the _PIC method in ACPI called a function that directly
accessed PCI config registers via the MCFG mapping to clear a bit when enabling
APIC mode. However, since the BIOS didn't use PCI config space but directly
accessed MCFG directly via SystemMemory, AcpiOsMapMemory was used to map MCFG.
This called pmap_mapbios() which remapped the MCFG window as Write-Back instead
of UC and the laptops hung right after this. The fix is to add yet another
variant of pmap_mapdev() which leaves the existing PAT mode alone and doesn't
change it and change AcpiOsMapMemory to use that instead of pmap_mapbios.
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