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Allow guest device MMIO access from bootmem memory segments.
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Authored by grehan on Aug 5 2020, 11:25 AM.

Details

Summary

Recent versions of UEFI have moved local APIC timer initialization into
the early SEC phase which runs out of ROM, prior to self-relocating
into RAM. This results in a hypervisor exit.

Currently bhyve prevents instruction emulation from segments that aren't
marked as "sysmem" aka guest RAM, with the vm_gpa_hold() routine failing.
However, there is no reason for this restriction: the hypervisor already
controls whether EPT mappings are marked as executable.

Fix by dropping the redundant check of sysmem.

(Note: this problem was first seen by D Scott Phillips and worked around in
UEFI by moving APIC initialization to the later PEI phase
github.com/freebsd/uefi-edk2/pull/7/commits/e8c6872573cd6c8642b0ed2fbeb5c08433dba21b

Test Plan

Boot the most recent bcran UEFI snapshot.

Diff Detail

Repository
rS FreeBSD src repository
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Unit
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Build Status
Buildable 32767
Build 30202: arc lint + arc unit