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

[Yeoreum Yun <yeoreum.yun@arm.com>]

> 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.

[...]

Thanks.

-- 
Sincerely,
Yeoreum Yun