KVM on ARM refuses to decode load/store instructions used to perform
I/O to emulated devices, and instead relies on the exception syndrome
information to describe the operand register, access size, etc.
This is only possible for instructions that have a single input/output
register (as opposed to ones that increment the offset register, or
load/store pair instructions, etc). Otherwise, QEMU crashes with the
following error
error: kvm run failed Function not implemented
R00=01010101 R01=00000008 R02=00000048 R03=08000820
R04=00000120 R05=7faaa0e0 R06=7faaa0dc R07=7faaa0e8
R08=7faaa0ec R09=7faaa088 R10=000000ff R11=00000080
R12=ff000000 R13=7fccfe08 R14=7faa835f R15=7faa887c
PSR=800001f3 N--- T svc32
QEMU: Terminated
and KVM produces a warning such as the following in the kernel log
kvm [17646]: load/store instruction decoding not implemented
The IoLib implementation provided by MdePkg/Library/BaseIoLibIntrinsic
is based on C code, and when LTO is in effect, the MMIO accesses could
be merged with, e.g., manipulations of the loop counter, producing
opcodes that KVM does not support for emulated MMIO.
So let's add a special ArmVirt flavor of this library that implements
that actual load/store operations in assembler, ensuring that the
instructions involved can be emulated by KVM.
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Ard Biesheuvel