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.

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?

> 
> > even before FF-A version negotiation since handler’s purpose seems to hook
> > certain memory operations, and DIRECT_MSG_REQ has been available
> > since FF-A specification v1.0.
> > 
> > Any feedback or alternative suggestions would be appreciated!
> > 
> > Link: https://lore.kernel.org/all/20260422162449.1814615-1-yeoreum.yun@arm.com/ [0]
> > 
> > Yeoreum Yun (3):
> >   arm64: KVM: defer kvm_init() to finalise_pkvm() when pKVM is enabled
> >   firmware: arm_ffa: initialise ff-a after finalising pKVM
> >     initialisation
> >   security: integrity: call load_uefi_certs() at late_initcall_sync
> > 
> >  arch/arm64/kvm/arm.c                          |   8 +-
> >  arch/arm64/kvm/pkvm.c                         |  15 ++-
> >  drivers/firmware/arm_ffa/bus.c                | 125 +++++++++++++++++-
> >  drivers/firmware/arm_ffa/common.h             |  13 +-
> >  drivers/firmware/arm_ffa/driver.c             |  21 ++-
> >  drivers/firmware/arm_ffa/smccc.c              |   2 +-
> >  security/integrity/platform_certs/load_uefi.c |   2 +-
> >  7 files changed, 166 insertions(+), 20 deletions(-)
> > 
> > 
> > base-commit: 7fd2df204f342fc17d1a0bfcd474b24232fb0f32
> 

-- 
Sincerely,
Yeoreum Yun