linux-kernel - Re: [PATCH v3 14/17] KVM: arm64: FFA: Remove access of endpoint memory access descriptor array

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Message-ID: <86leciog2w.wl-maz@kernel.org>
Date:   Wed, 04 Oct 2023 11:08:23 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Marc Bonnici <marc.bonnici@....com>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Coboy Chen <coboy.chen@...iatek.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Olivier Deprez <olivier.deprez@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Will Deacon <will@...nel.org>,
        Quentin Perret <qperret@...gle.com>
Subject: Re: [PATCH v3 14/17] KVM: arm64: FFA: Remove access of endpoint memory access descriptor array

On Fri, 29 Sep 2023 16:03:03 +0100,
Sudeep Holla <sudeep.holla@....com> wrote:
> 
> FF-A v1.1 removes the fixed location of endpoint memory access descriptor
> array within the memory transaction descriptor structure. In preparation
> to remove the ep_mem_access member from the ffa_mem_region structure,
> provide the accessor to fetch the offset and use the same in FF-A proxy
> implementation.
> 
> The accessor take the boolean argument that indicates if the memory access
> descriptor versions is v1(old format) or not. Currently it is set true as
> FF-A proxy supports only v1.0
> 
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Oliver Upton <oliver.upton@...ux.dev>
> Cc: Will Deacon <will@...nel.org>
> Cc: Quentin Perret <qperret@...gle.com>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>  arch/arm64/kvm/hyp/nvhe/ffa.c | 8 ++++++--
>  include/linux/arm_ffa.h       | 6 ++++++
>  2 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index 6e4dba9eadef..5f956f53e6bf 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> @@ -423,6 +423,7 @@ static __always_inline void do_ffa_mem_xfer(const u64 func_id,
>  	DECLARE_REG(u32, fraglen, ctxt, 2);
>  	DECLARE_REG(u64, addr_mbz, ctxt, 3);
>  	DECLARE_REG(u32, npages_mbz, ctxt, 4);
> +	struct ffa_mem_region_attributes *ep_mem_access;
>  	struct ffa_composite_mem_region *reg;
>  	struct ffa_mem_region *buf;
>  	u32 offset, nr_ranges;
> @@ -452,7 +453,8 @@ static __always_inline void do_ffa_mem_xfer(const u64 func_id,
>  	buf = hyp_buffers.tx;
>  	memcpy(buf, host_buffers.tx, fraglen);
>  
> -	offset = buf->ep_mem_access[0].composite_off;
> +	ep_mem_access = (void *)buf + ffa_mem_desc_offset(buf, 0, true);
> +	offset = ep_mem_access->composite_off;
>  	if (!offset || buf->ep_count != 1 || buf->sender_id != HOST_FFA_ID) {
>  		ret = FFA_RET_INVALID_PARAMETERS;
>  		goto out_unlock;
> @@ -504,6 +506,7 @@ static void do_ffa_mem_reclaim(struct arm_smccc_res *res,
>  	DECLARE_REG(u32, handle_lo, ctxt, 1);
>  	DECLARE_REG(u32, handle_hi, ctxt, 2);
>  	DECLARE_REG(u32, flags, ctxt, 3);
> +	struct ffa_mem_region_attributes *ep_mem_access;
>  	struct ffa_composite_mem_region *reg;
>  	u32 offset, len, fraglen, fragoff;
>  	struct ffa_mem_region *buf;
> @@ -528,7 +531,8 @@ static void do_ffa_mem_reclaim(struct arm_smccc_res *res,
>  	len = res->a1;
>  	fraglen = res->a2;
>  
> -	offset = buf->ep_mem_access[0].composite_off;
> +	ep_mem_access = (void *)buf + ffa_mem_desc_offset(buf, 0, true);
> +	offset = ep_mem_access->composite_off;
>  	/*
>  	 * We can trust the SPMD to get this right, but let's at least
>  	 * check that we end up with something that doesn't look _completely_
> diff --git a/include/linux/arm_ffa.h b/include/linux/arm_ffa.h
> index 748d0a83a4bc..7be240e37f36 100644
> --- a/include/linux/arm_ffa.h
> +++ b/include/linux/arm_ffa.h
> @@ -357,6 +357,12 @@ struct ffa_mem_region {
>  #define CONSTITUENTS_OFFSET(x)	\
>  	(offsetof(struct ffa_composite_mem_region, constituents[x]))
>  
> +static inline u32
> +ffa_mem_desc_offset(struct ffa_mem_region *buf, int count, bool mem_desc_v1)
> +{
> +	return COMPOSITE_OFFSET(0);
> +}

If the goal of this patch is to introduce some versioning, why not
define this last parameter as an actual version number, PSCI style
(with a minor and major, each on a 16bit field)?

Even the name is pretty misleading, as both FFA versions are v1 (v1.0
vs v1.1...).

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.