Re: [PATCH] ArmVirtPkg: implement KVM safe IoLib instance

[Leif Lindholm <leif.lindholm@linaro.org>]

On Tue, Jun 05, 2018 at 01:05:43PM +0200, Ard Biesheuvel wrote:
> 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 instead, let's reimplement IoLib in a KVM safe manner.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
> Yet another approach for the KVM MMIO emulation issue. Note that this one
> (as well as the MdePkg) affect both AArch64 and ARM. This is deliberate,
> given that there is no reason AArch64 should be immune to this: we simply
> haven't triggered the issue yet.

I'm happier with this version (at the same time as I'm sad we're
splitting this out).

Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>

>  ArmVirtPkg/Library/ArmVirtIoLib/AArch64/ArmVirtMmio.S |  164 ++
>  ArmVirtPkg/Library/ArmVirtIoLib/Arm/ArmVirtMmio.S     |  154 ++
>  ArmVirtPkg/Library/ArmVirtIoLib/Arm/ArmVirtMmio.asm   |  165 ++
>  ArmVirtPkg/Library/ArmVirtIoLib/ArmVirtIoLib.c        |  589 +++++
>  ArmVirtPkg/Library/ArmVirtIoLib/ArmVirtIoLib.h        |  188 ++
>  ArmVirtPkg/Library/ArmVirtIoLib/ArmVirtIoLib.inf      |   49 +
>  ArmVirtPkg/Library/ArmVirtIoLib/IoHighLevel.c         | 2358 ++++++++++++++++++++
>  ArmVirtPkg/Library/ArmVirtIoLib/IoLibMmioBuffer.c     |  413 ++++
>  8 files changed, 4080 insertions(+)