c45cbc7a1f
Previously, AcpiOsMemory was using pmap_mapbios which would always map the requested address Write-Back (WB). For several AMD Ryzen laptops, the BIOS uses AcpiOsMemory to directly access the PCI MCFG region in order to access PCI config registers. This has the side effect of remapping the MCFG region in the direct map as WB instead of UC hanging the laptops during boot. On the one laptop I examined in detail, the _PIC global method used to switch from 8259A PICs to I/O APICs uses a pair of PCI config space registers at offset 0x84 in the device at 0:0:0 to as a pair of address/data registers to access an indirect register in the chipset and clear a single bit to switch modes. To fix, alter the semantics of pmap_mapbios() such that it does not modify the attributes of any existing mappings and instead uses the existing attributes. If a new mapping is created, this new mapping uses WB (the default memory attribute). Special thanks to the gentleman whose name I don't have who brought two affected laptops to the hacker lounge at BSDCan. Direct access to the affected systems permitted finding the root cause within an hour or so. PR: 231760, 236899 Reviewed by: kib, alc MFC after: 2 weeks Differential Revision: https://reviews.freebsd.org/D20327 |
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| .. | ||
| acpica | ||
| bios | ||
| cloudabi32 | ||
| conf | ||
| i386 | ||
| include | ||
| linux | ||
| pci | ||
| Makefile | ||