Ruben Hakobyan eb75a4ead7 arch: x86_64: Set GuestPhysAddrSize in CPUID leaf 0x80000008 ...

When generating guest CPUID, we set PhysAddrSize (EAX bits 7:0)
based on the host's physical address bits. On AMD hosts with SME,
get_host_cpu_phys_bits() subtracts the c-bit reduction from this
value, but the code here only writes the result to bits 7:0 and
leaves GuestPhysAddrSize (bits 23:16) at the unmodified host value.
This creates a gap: e.g. PhysAddrSize=43 but GuestPhysAddrSize=48.

Guest firmware that reads GuestPhysAddrSize will see a larger
address space than the VMM provides, and may place PCI BARs beyond
the MMIO bus range. However, Cloud-hypervisor sizes its MMIO bus to
phys_bits.

Fix by setting both PhysAddrSize (bits 7:0) and GuestPhysAddrSize
(bits 23:16) to phys_bits, using mask 0xff00_ff00 instead of
0xffff_ff00.

Signed-off-by: Ruben Hakobyan <hruben@meta.com>

2026-05-29 12:04:47 +00:00

..

src

arch: x86_64: Set GuestPhysAddrSize in CPUID leaf 0x80000008

2026-05-29 12:04:47 +00:00

Cargo.toml

arch: Helper functions for u32 hex (de-) serialization

2026-05-28 15:19:15 +00:00