Re: [edk2-devel] [PATCH 2/3] ArmVirtPkg/ArmVirtQemu: Expose TRNG hypercall via RngDxe if implemented

["PierreGondois" <pierre.gondois@arm.com>]

On 1/11/23 17:49, Ard Biesheuvel wrote:
> On Fri, 18 Nov 2022 at 17:48, PierreGondois <pierre.gondois@arm.com> wrote:
>>
>> Hello Ard,
>>
>> On 11/10/22 14:47, Ard Biesheuvel wrote:
>>> Currently, we only expose the EFI_RNG_PROTOCOL in ArmVirtQemu if QEMU
>>> provides a virtio-rng device, and it doesn't do so by default.
>>>
>>> Given that KVM exposes the ARM architected TRNG service (and has done so
>>> for a while now), let's incorporate the RngDxe driver which has recently
>>> grown support for the ARM firmware/hypervisor service.
>>>
>>> If both the service and the virtio device are available, two
>>> implementations of the RNG protocol will be exposed, but this is fine:
>>> callers that don't care about the distinction will grab the first one
>>> available.
>>>
>>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>>> ---
>>>    ArmVirtPkg/ArmVirtQemu.dsc           | 11 +++++++++++
>>>    ArmVirtPkg/ArmVirtQemuFvMain.fdf.inc |  5 +++++
>>>    ArmVirtPkg/ArmVirtQemuKernel.dsc     | 11 +++++++++++
>>>    3 files changed, 27 insertions(+)
>>>
>>> diff --git a/ArmVirtPkg/ArmVirtQemu.dsc b/ArmVirtPkg/ArmVirtQemu.dsc
>>> index f77443229e8e..1771ad562225 100644
>>> --- a/ArmVirtPkg/ArmVirtQemu.dsc
>>> +++ b/ArmVirtPkg/ArmVirtQemu.dsc
>>> @@ -140,6 +140,8 @@ [PcdsFeatureFlag.common]
>>>
>>>      gArmVirtTokenSpaceGuid.PcdTpm2SupportEnabled|$(TPM2_ENABLE)
>>>
>>> +  gArmTokenSpaceGuid.PcdMonitorConduitHvc|TRUE
>>> +
>>
>> It seems that the PSCI conduit needs to be dynamically set.
> 
> Why? And how is this different from PSCI for resetting the system?

The PSCI implementation used for ArmVirtQemu is parsing the conduit
to use, so it can handle both cases:
https://github.com/tianocore/edk2/blob/fe405f08a09e9f2306c72aa23d8edfbcfaa23bff/ArmVirtPkg/Library/ArmVirtPsciResetSystemLib/ArmVirtPsciResetSystemLib.c#L49

> 
> Note that ArmVIrtQemu was never intended to run at EL2, even if it
> seems to work to some extent.

Ok understood.

> 
> 
>> The psci conduit that should be used is configured by qemu depending on the
>> virtualization=[on|off] parameter. When off, HVC must be used (SMC otherwise).
>> Cf:
>> https://github.com/qemu/qemu/blob/master/hw/arm/virt.c#L2052

(replacing with a permanent link)
https://github.com/qemu/qemu/blob/aa96ab7c9df59c615ca82b49c9062819e0a1c287/hw/arm/virt.c#L2080

>>
>> If using the wrong conduit, qemu traps the instruction and stops.
>> For KvmTool, the conduit is always HVC.
>>
>> Command used:
>> [PATH_TO]/qemu/build/qemu-system-aarch64 \
>>          -serial stdio -M virt,highmem=on,virtualization=off \
>>          -cpu cortex-a57 -smp 4 -m 4096 \
>>          -drive file=pflash0.img,format=raw,if=pflash,readonly=on \
>>          -drive file=pflash1.img,format=raw,if=pflash
>>
>> Regards,
>> Pierre
>>
>>
>> 
>>
>>