Re: [RFC PATCH 0/3] initalise ff-a after finalising pKVM

[Ben Horgan <ben.horgan@arm.com>]

Hi Levi,

On 5/5/26 12:16, Yeoreum Yun wrote:
>> Hi Ben,
>>
>>> Hi Levi,
>>>
>>> On 5/5/26 10:54, Yeoreum Yun wrote:
>>>> This patch is split out from the patchset [0] --
>>>> fix FF-A call failure with pKVM when the FF-A driver is built-in,
>>>> specifically the IMA-related part.
>>>>
>>>> When pKVM is enabled, the FF-A driver must be initialised after pKVM.
>>>> Otherwise, pKVM cannot negotiate the FF-A version or obtain the RX/TX
>>>> buffer information, leading to failures in FF-A calls.
>>>>
>>>> Currently, pKVM initialisation completes at device_initcall_sync,
>>>> while ffa_init() runs at the device_initcall level.
>>>>
>>>> So far, linker deployes kvm_arm_init() before ffa_init(), and SMCs can
>>>> still be trapped even before finalise_pkvm() is invoked.
>>>> As a result, this issue has not been observed.
>>>>
>>>> However, relying on above stuff is fragile.
>>>> Therefore, when pKVM is enabled, the FF-A infrastructure should be
>>>> initialised only after pKVM initialisation has been fully finalised.
>>>>
>>>> To achieve this, introduce an ffa_root_dev ("arm-ffa") and
>>>> a corresponding driver to defer initialisation of the FF-A infrastructure
>>>> until pKVM initialisation is complete, and to defer probing of all FF-A devices until then
>>>> when pKVM is enabled.
>>>>
>>>> This patch is based on v7.1-rc2
>>>>
>>>> Question:
>>>>
>>>> FF-A initialisation can occur at late_initcall. Because it may be deferred,
>>>> some FF-A requests cannot be serviced at that stage.
>>>> A typical example is the EFI runtime variable service using DIRECT_MSG_REQ.
>>>>
>>>> Depending on the platform, the EFI runtime variable service runs with StandaloneMm
>>>> and uses FF-A DIRECT_REQ. However, when pKVM is enabled, FF-A initialisation
>>>> may be deferred to late_initcall. In this case, load_uefi_certs()
>>>> can fail if it is invoked before the FF-A driver is initialised
>>>> via deferred_probe_initcall().
>>>>
>>>> Moving load_uefi_certs() to late_initcall_sync, as in the third patch,
>>>> seems not to have any problem since late_initcall and
>>>> late_initcall_sync are both of do_basic_setup() and it's before loading
>>>> init process. However, it is still unclear whether
>>>> it would be better to allow DIRECT_MSG_REQ in kvm_host_ffa_handler()
>>>
>>> The spec doesn't allow this. Looking at DEN0077A 1.2 REL0:
>>>
>>> Section 13.2.2 says:
>>>
>>> "If they are compatible, it enables them to determine which Framework functionalities can be used. Hence, negotiation of
>>> the version must happen before an invocation of any other FF-A ABI."
>>>
>>> and a bit further down
>>>
>>> "Once the caller invokes any FF-A ABI other than FFA_VERSION, the version negotiation phase is complete."
>>>
>>> I would have thought that an SP would only go into the waiting state once the version negotiation is done.
>>
>> I mean the negotiation between hypervisor and ff-a driver.
>> actually the version negotiation is done with SPMC in
>> hyp_ffa_init() but the negotiaion between hypervisor and ff-a driver
>> just choose the lower version between version requested from ff-a driver
>> and negotiated version with hypervisor and SPMC.
> 
> Sorry. re-parse the word, not choose "re-negotiate" when
> FF-A driver request lowever version.
> 
>>
>> So, the version negotiation is already done with SPMC
>> but with FF-A driver with hypervisor is not yet.
>> However, DIRECT_MSG_REQ has supported from v1.0 
>> In this situation, is there any reason not to send DIRECT_REQ_MSG?
> 
> IOW, question is that some of ff-a request can be allowed
> before version negotiation with FF-A driver but
> using negotiated version via hyp_ffa_init() first or not.

I don't think so. Isn't it more a continuation of the negotiation rather than a re-negotiation?

Thanks,

Ben

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> Thanks.
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