linux-kernel - Re: [PATCH v2 3/4] KVM: arm64: Map the hypervisor FF-A buffers on ffa init

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Message-ID: <Z8ZPBZF7J-qKdb_i@google.com>
Date: Tue, 4 Mar 2025 00:53:25 +0000
From: Sebastian Ene <sebastianene@...gle.com>
To: Will Deacon <will@...nel.org>
Cc: catalin.marinas@....com, joey.gouly@....com, maz@...nel.org,
	oliver.upton@...ux.dev, snehalreddy@...gle.com,
	sudeep.holla@....com, suzuki.poulose@....com, vdonnefort@...gle.com,
	yuzenghui@...wei.com, kvmarm@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel-team@...roid.com
Subject: Re: [PATCH v2 3/4] KVM: arm64: Map the hypervisor FF-A buffers on
 ffa init

On Mon, Mar 03, 2025 at 11:43:03PM +0000, Will Deacon wrote:
> On Thu, Feb 27, 2025 at 06:17:48PM +0000, Sebastian Ene wrote:
> > Map the hypervisor's buffers irrespective to the host and return
> > a linux error code from the FF-A error code on failure. Remove
> > the unmap ff-a buffers calls from the hypervisor as it will
> > never be called.
> > Prevent the host from using FF-A directly with Trustzone
> > if the hypervisor could not map its own buffers.
> > 
> > Signed-off-by: Sebastian Ene <sebastianene@...gle.com>
> > ---
> >  arch/arm64/kvm/hyp/nvhe/ffa.c | 46 +++++++++++++----------------------
> >  1 file changed, 17 insertions(+), 29 deletions(-)
> 
> [...]
> 
> > @@ -861,6 +842,7 @@ int hyp_ffa_init(void *pages)
> >  {
> >  	struct arm_smccc_res res;
> >  	void *tx, *rx;
> > +	int ret;
> >  
> >  	if (kvm_host_psci_config.smccc_version < ARM_SMCCC_VERSION_1_2)
> >  		return 0;
> > @@ -911,5 +893,11 @@ int hyp_ffa_init(void *pages)
> >  		.lock	= __HYP_SPIN_LOCK_UNLOCKED,
> >  	};
> >  
> > +	/* Map our hypervisor buffers into the SPMD */
> > +	ret = ffa_map_hyp_buffers();
> > +	if (ret)
> > +		return ret;
> 
> Doesn't calling RXTX_MAP here undo the fix from c9c012625e12 ("KVM:
> arm64: Trap FFA_VERSION host call in pKVM") where we want to allow for
> the host to negotiate the version lazily?

We still have the same behaviour where we don't allow memory
sharing to happen until the version is negotiated but this
separates the hypervisor buffer mapping part from the host.

> 
> Will

Thanks,
Sebastian