Re: [PATCH v3 1/2] MdePkg/BaseIoLibIntrinsic: make BaseIoLibIntrinsic safe for ArmVirt/KVM

[Laszlo Ersek <lersek@redhat.com>]

On 06/11/18 09:25, 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 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>
> ---
> v3: add missing prototype comments in IoLibArmVirt.c
>     remove mention of ASSERT () from description of internal asm routines
> v2: add missing .uni file
>     split off ArmVirtPkg change
>     add VS2017 version of AArch64 asm file
>     add reference to MdePkg.dsc
> 
>  MdePkg/Library/BaseIoLibIntrinsic/AArch64/ArmVirtMmio.S         | 148 ++++
>  MdePkg/Library/BaseIoLibIntrinsic/AArch64/ArmVirtMmio.asm       | 149 ++++
>  MdePkg/Library/BaseIoLibIntrinsic/Arm/ArmVirtMmio.S             | 145 ++++
>  MdePkg/Library/BaseIoLibIntrinsic/Arm/ArmVirtMmio.asm           | 149 ++++
>  MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsicArmVirt.inf |  52 ++
>  MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsicArmVirt.uni |  23 +
>  MdePkg/Library/BaseIoLibIntrinsic/IoLibArmVirt.c                | 733 ++++++++++++++++++++
>  MdePkg/MdePkg.dsc                                               |   1 +
>  8 files changed, 1400 insertions(+)

Acked-by: Laszlo Ersek <lersek@redhat.com>