Hi Sami,
On Tue, Feb 02, 2021 at 10:40:32AM +0000, Sami Mujawar wrote:
> Hi Ilias,
>
> Please see my response inline marked [SAMI].
>
> Regards,
>
> Sami Mujawar
>
> -----Original Message-----
> From: Ilias Apalodimas <ilias.apalodi...@linaro.org>
> Sent: 01 February 2021 02:01 PM
> To: Sami Mujawar <sami.muja...@arm.com>
> Cc: Sughosh Ganu <sughosh.g...@linaro.org>; devel@edk2.groups.io; Ard
> Biesheuvel <ard.biesheu...@arm.com>; Leif Lindholm <l...@nuviainc.com>; Sahil
> Malhotra <sahil.malho...@linaro.org>
> Subject: Re: [PATCH edk2-platforms v3 1/2] Drivers/OpTeeRpmb: Add an OP-TEE
> backed RPMB driver
>
> Hi Sami,
>
>
> [...]
> > > +STATIC
> > > +EFI_STATUS
> > > +ReadWriteRpmb (
> > > + UINTN SvcAct,
> > > + UINTN Addr,
> > > + UINTN NumBytes,
> > > + UINTN Offset
> > > + )
> > > +{
> > > + ARM_SVC_ARGS SvcArgs;
> > > + EFI_STATUS Status;
> > > +
> > > + ZeroMem (&SvcArgs, sizeof (SvcArgs));
> > > +
> > > + SvcArgs.Arg0 = ARM_SVC_ID_FFA_MSG_SEND_DIRECT_REQ_AARCH64;
> > > + SvcArgs.Arg1 = storage_id;
> > > + SvcArgs.Arg2 = 0;
> > > + SvcArgs.Arg3 = SvcAct;
> > > + SvcArgs.Arg4 = Addr;
> > > + SvcArgs.Arg5 = NumBytes;
> > > + SvcArgs.Arg6 = Offset;
> > > +
> > > + ArmCallSvc (&SvcArgs);
> > > + if (SvcArgs.Arg3) {
> > > + DEBUG ((DEBUG_ERROR, "%a: Svc Call 0x%08x Addr: 0x%08x len: 0x%x
> > > Offset: 0x%x failed with 0x%x\n",
> > > + __func__, SvcAct, Addr, NumBytes, Offset, SvcArgs.Arg3));
> > > + }
> > > +
> > > + switch (SvcArgs.Arg3) {
> > > + case ARM_SVC_SPM_RET_SUCCESS:
> > > + Status = EFI_SUCCESS;
> > > + break;
> > > +
> > > + case ARM_SVC_SPM_RET_NOT_SUPPORTED:
> > > + Status = EFI_UNSUPPORTED;
> > > + break;
> > > +
> > > + case ARM_SVC_SPM_RET_INVALID_PARAMS:
> > > + Status = EFI_INVALID_PARAMETER;
> > > + break;
> > > +
> > > + case ARM_SVC_SPM_RET_DENIED:
> > > + Status = EFI_ACCESS_DENIED;
> > > + break;
> > > +
> > > + case ARM_SVC_SPM_RET_NO_MEMORY:
> > > + Status = EFI_BAD_BUFFER_SIZE;
> > > + break;
> > > +
> > > + default:
> > > + Status = EFI_ACCESS_DENIED;
> > > + }
> > > [SAMI] Should the error handling here be updated similar to the FF-A
> > > StandaloneMmPkg patches?
> > > [/SAMI]
> >
> > I actually picked up the error handling from the previous non-FFA code.
> > I'll check what's on Sughosh latest patches and fix it if there are
> > any differences.
> > Looking at it again EFI_BAD_BUFFER_SIZE can change to indicate out of
> > memory properly anyway.
> >
>
> Had another look at this. This seems fine if I just change
> EFI_BAD_BUFFER_SIZE -> EFI OUT_OF_RESOURCES because OP-TEE is only
> using these errors from FFA. Eventually the OP-TEE code that launches
> StMM today, will move to FFA and become a separate SP, so that will
> naturally be handled once that's done. I don't see a point of adding
> unused error cases.
>
> [SAMI] Referring to the FFA specification, DEN0077A, v1.0, section 10.2
> FFA_MSG_SEND_DIRECT_REQ and Table 10.8: FFA_ERROR encoding, I think the
> error codes being handled above would be returned in SvcArgs.Arg2.
Hmm why ?
> The message flow would be as follows:
> - Caller sends FFA_MSG_SEND_DIRECT_REQ to the target endpoint.
> - if the message does not reach the target endpoint, an error code from
> Table 10.8 may be returned in w2 (i.e. SvcArgs.Arg2)
That would be in the case you have a working TF-A implementation and the
message is never dispatched to the endpoint right?
The current driver is not implementing the whole range of that spec. The
communication between secure/non secure world is still based on the OP-TEE
messaging mechanism.
The only part that complies to the FFA spec is the communication between the
driver itself and OP-TEE.
> - If the message reaches the target endpoint, then callee shall invoke
> one of the following interfaces:
> * FFA_MSG_SEND_DIRECT_RESP
So what's happening here, is that we send an SVC with
ARM_SVC_ID_FFA_MSG_SEND_DIRECT_REQ_AARCH64.
The op-tee relevant code is located at ./core/arch/arm/kernel/stmm_sp.c
There's 2 things we handle right now on OP-TEE:
1. set the page permissions, after relocating the executable.
2. Read/Write data on our RPMB.
In both cases service_compose_direct_resp() is used to construct the response
and that set the return value on x3.
Regards
/Ilias
> * FFA_INTERRUPT
> * FFA_SUCCESS
> This would mean that if the callee responds with
> FFA_MSG_SEND_DIRECT_RESP, the callee returned error/status code shall be in
> w/x3-w/x7 (which I think in this case may be in SvcArgs.Arg3).
> [/SAMI]
>
> Regards
> /Ilias
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