Re: [PATCH v2 6/6] xen/arm: ffa: Deliver VM-to-VM notifications locally

[Jens Wiklander <jens.wiklander@xxxxxxxxxx>]

Hi Bertrand,

On Mon, May 11, 2026 at 3:17 PM Bertrand Marquis
<Bertrand.Marquis@xxxxxxx> wrote:
>
> Hi Jens,
>
> > On 5 May 2026, at 11:21, Jens Wiklander <jens.wiklander@xxxxxxxxxx> wrote:
> >
> > Hi Bertrand,
> >
> > On Wed, Apr 29, 2026 at 7:44 AM Bertrand Marquis
> > <bertrand.marquis@xxxxxxx> wrote:
> >>
> >> VM notification binding and pending tracking exist for non-secure
> >> endpoints, but FFA_NOTIFICATION_SET still only forwards secure
> >> destinations to the SPMC. Non-secure VMs therefore cannot receive
> >> notifications from other VMs. Local NPI delivery also needs explicit
> >> re-arm tracking so repeated raises are not lost while the interrupt is
> >> already pending.
> >>
> >> Add a local VM notification delivery path for non-secure destinations.
> >> notification_set_vm() resolves the destination endpoint, verifies that
> >> every requested bit is bound to the sender, sets the receiver's
> >> vm_pending bitmap under notif_lock, and raises an NPI only when local
> >> pending state is not already armed.
> >>
> >> Track whether a local NPI is already armed with notif_irq_raised,
> >> clear that state once both VM and hypervisor pending bitmaps are
> >> drained, and keep notif_lock held across the VM notification injection
> >> attempt. If no destination vCPU is online, leave the pending bits set
> >> and keep notif_irq_raised clear so delivery can be retried later.
> >> Also expose firmware notification availability so FFA_FEATURES only
> >> advertises notification support when it is actually provided by the
> >> firmware or by CONFIG_FFA_VM_TO_VM.
> >>
> >> Functional impact: when CONFIG_FFA_VM_TO_VM is enabled, non-secure
> >> FFA_NOTIFICATION_SET delivers VM-to-VM notifications locally and keeps
> >> NPI delivery reliable across repeated raises.
> >>
> >> Signed-off-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> >> ---
> >> Changes since v1:
> >> - serialize notification_set_vm() state updates with the NPI attempt
> >> - keep pending VM notifications set when local injection fails
> >> ---
> >> xen/arch/arm/tee/ffa.c         | 24 ++++++++--
> >> xen/arch/arm/tee/ffa_notif.c   | 82 ++++++++++++++++++++++++++++++++--
> >> xen/arch/arm/tee/ffa_private.h | 17 ++++---
> >> 3 files changed, 107 insertions(+), 16 deletions(-)
> >>
> >> diff --git a/xen/arch/arm/tee/ffa.c b/xen/arch/arm/tee/ffa.c
> >> index 1fe33f26454a..7fe021049cba 100644
> >> --- a/xen/arch/arm/tee/ffa.c
> >> +++ b/xen/arch/arm/tee/ffa.c
> >> @@ -39,8 +39,13 @@
> >>  * o FFA_MSG_SEND_DIRECT_REQ:
> >>  *   - only supported from a VM to an SP
> >>  * o FFA_NOTIFICATION_*:
> >> + *   - only supported when firmware notifications are enabled or VM-to-VM
> >> + *     support is built in
> >>  *   - only supports global notifications, that is, per vCPU notifications
> >> - *     are not supported
> >> + *     are not supported and secure per-vCPU notification information is
> >> + *     not forwarded
> >> + *   - the source endpoint ID reported for a notification may no longer
> >> + *     exist by the time the receiver consumes it
> >>  *   - doesn't support signalling the secondary scheduler of pending
> >>  *     notification for secure partitions
> >>  *   - doesn't support notifications for Xen itself
> >> @@ -245,6 +250,8 @@ static void handle_features(struct cpu_user_regs *regs)
> >>     uint32_t a1 = get_user_reg(regs, 1);
> >>     struct domain *d = current->domain;
> >>     struct ffa_ctx *ctx = d->arch.tee;
> >> +    bool notif_supported = IS_ENABLED(CONFIG_FFA_VM_TO_VM) ||
> >> +                           ffa_notif_fw_enabled();
> >>
> >>     /*
> >>      * FFA_FEATURES defines w2 as input properties only for specific
> >> @@ -343,10 +350,16 @@ static void handle_features(struct cpu_user_regs 
> >> *regs)
> >>
> >>         break;
> >>     case FFA_FEATURE_NOTIF_PEND_INTR:
> >> -        ffa_set_regs_success(regs, GUEST_FFA_NOTIF_PEND_INTR_ID, 0);
> >> +        if ( notif_supported )
> >> +            ffa_set_regs_success(regs, GUEST_FFA_NOTIF_PEND_INTR_ID, 0);
> >> +        else
> >> +            ffa_set_regs_error(regs, FFA_RET_NOT_SUPPORTED);
> >>         break;
> >>     case FFA_FEATURE_SCHEDULE_RECV_INTR:
> >> -        ffa_set_regs_success(regs, GUEST_FFA_SCHEDULE_RECV_INTR_ID, 0);
> >> +        if ( notif_supported )
> >> +            ffa_set_regs_success(regs, GUEST_FFA_SCHEDULE_RECV_INTR_ID, 
> >> 0);
> >> +        else
> >> +            ffa_set_regs_error(regs, FFA_RET_NOT_SUPPORTED);
> >>         break;
> >>     case FFA_PARTITION_INFO_GET_REGS:
> >>         if ( ACCESS_ONCE(ctx->guest_vers) >= FFA_VERSION_1_2 )
> >> @@ -361,7 +374,10 @@ static void handle_features(struct cpu_user_regs 
> >> *regs)
> >>     case FFA_NOTIFICATION_SET:
> >>     case FFA_NOTIFICATION_INFO_GET_32:
> >>     case FFA_NOTIFICATION_INFO_GET_64:
> >> -        ffa_set_regs_success(regs, 0, 0);
> >> +        if ( notif_supported )
> >> +            ffa_set_regs_success(regs, 0, 0);
> >> +        else
> >> +            ffa_set_regs_error(regs, FFA_RET_NOT_SUPPORTED);
> >>         break;
> >>     default:
> >>         ffa_set_regs_error(regs, FFA_RET_NOT_SUPPORTED);
> >> diff --git a/xen/arch/arm/tee/ffa_notif.c b/xen/arch/arm/tee/ffa_notif.c
> >> index a841c8f8d747..b29d948a7110 100644
> >> --- a/xen/arch/arm/tee/ffa_notif.c
> >> +++ b/xen/arch/arm/tee/ffa_notif.c
> >> @@ -21,6 +21,11 @@ static bool __ro_after_init fw_notif_enabled;
> >> static unsigned int __ro_after_init notif_sri_irq;
> >> static DEFINE_SPINLOCK(notif_info_lock);
> >>
> >> +bool ffa_notif_fw_enabled(void)
> >> +{
> >> +    return fw_notif_enabled;
> >> +}
> >> +
> >> static bool inject_notif_pending(struct domain *d)
> >> {
> >>     struct vcpu *v;
> >> @@ -107,6 +112,55 @@ out_unlock:
> >>     return ret;
> >> }
> >>
> >> +/*
> >> + * Deliver a VM-to-VM notification. ctx->notif.notif_lock protects
> >> + * vm_bind/vm_pending so callers must not hold it already.
> >> + */
> >> +static int32_t notification_set_vm(uint16_t dst_id, uint16_t src_id,
> >> +                                   uint32_t flags, uint64_t bitmap)
> >> +{
> >> +    struct domain *dst_d;
> >> +    struct ffa_ctx *dst_ctx;
> >> +    unsigned int id;
> >> +    int32_t ret;
> >> +
> >> +    if ( flags )
> >> +        return FFA_RET_INVALID_PARAMETERS;
> >> +
> >> +    ret = ffa_endpoint_domain_lookup(dst_id, &dst_d, &dst_ctx);
> >> +    if ( ret )
> >> +        return ret;
> >> +
> >> +    ret = FFA_RET_OK;
> >> +
> >> +    spin_lock(&dst_ctx->notif.notif_lock);
> >> +
> >> +    for ( id = 0; id < FFA_NUM_VM_NOTIF; id++ )
> >> +    {
> >> +        if ( !(bitmap & BIT(id, ULL)) )
> >> +            continue;
> >> +
> >> +        if ( dst_ctx->notif.vm_bind[id] != src_id )
> >> +        {
> >> +            ret = FFA_RET_DENIED;
> >> +            goto out_unlock;
> >> +        }
> >> +    }
> >> +
> >> +    dst_ctx->notif.vm_pending |= bitmap;
> >> +    if ( !dst_ctx->notif.notif_irq_raised &&
> >> +         (dst_ctx->notif.vm_pending || dst_ctx->notif.hyp_pending) &&
> >> +         inject_notif_pending(dst_d) )
> >> +        dst_ctx->notif.notif_irq_raised = true;
> >> +
> >> +out_unlock:
> >> +    spin_unlock(&dst_ctx->notif.notif_lock);
> >> +
> >> +    rcu_unlock_domain(dst_d);
> >> +
> >> +    return ret;
> >> +}
> >> +
> >> int32_t ffa_handle_notification_bind(struct cpu_user_regs *regs)
> >> {
> >>     struct domain *d = current->domain;
> >> @@ -288,6 +342,8 @@ void ffa_handle_notification_get(struct cpu_user_regs 
> >> *regs)
> >>
> >>     if ( IS_ENABLED(CONFIG_FFA_VM_TO_VM) )
> >>     {
> >> +        bool pending;
> >> +
> >>         spin_lock(&ctx->notif.notif_lock);
> >>
> >>         if ( (flags & FFA_NOTIF_FLAG_BITMAP_HYP) && ctx->notif.hyp_pending 
> >> )
> >> @@ -298,6 +354,18 @@ void ffa_handle_notification_get(struct cpu_user_regs 
> >> *regs)
> >>                 ctx->notif.notif_irq_raised = false;
> >>         }
> >>
> >> +        if ( (flags & FFA_NOTIF_FLAG_BITMAP_VM) && ctx->notif.vm_pending )
> >> +        {
> >> +            w4 = (uint32_t)(ctx->notif.vm_pending & GENMASK(31, 0));
> >> +            w5 = (uint32_t)((ctx->notif.vm_pending >> 32) & GENMASK(31, 
> >> 0));
> >> +            ctx->notif.vm_pending = 0;
> >> +        }
> >> +
> >> +        pending = (ctx->notif.hyp_pending != 0) ||
> >> +                  (ctx->notif.vm_pending != 0);
> >> +        if ( !pending )
> >> +            ctx->notif.notif_irq_raised = false;
> >
> > This seems to take care of clearing notif_irq_raised for all cases. Do
> > we still need the one just above this block (copied here):
> >            if ( !ctx->notif.vm_pending )
> >                ctx->notif.notif_irq_raised = false;
> > ?
>
> Yes you are right, this is now redundant.
> I will drop it in v3.

Good, thanks.

Cheers,
Jens

>
> Cheers
> Bertrand
>
> >
> > Cheers,
> > Jens
> >
> >> +
> >>         spin_unlock(&ctx->notif.notif_lock);
> >>     }
> >>
> >> @@ -323,9 +391,17 @@ int32_t ffa_handle_notification_set(struct 
> >> cpu_user_regs *regs)
> >>     if ( flags )
> >>         return FFA_RET_INVALID_PARAMETERS;
> >>
> >> -    if ( FFA_ID_IS_SECURE(dest_id) && fw_notif_enabled )
> >> -        return ffa_simple_call(FFA_NOTIFICATION_SET, src_dst, flags, 
> >> bitmap_lo,
> >> -                               bitmap_hi);
> >> +    if ( FFA_ID_IS_SECURE(dest_id) )
> >> +    {
> >> +        if ( fw_notif_enabled )
> >> +            return ffa_simple_call(FFA_NOTIFICATION_SET, src_dst, flags,
> >> +                                   bitmap_lo, bitmap_hi);
> >> +    }
> >> +    else if ( IS_ENABLED(CONFIG_FFA_VM_TO_VM) )
> >> +    {
> >> +        return notification_set_vm(dest_id, caller_id, flags,
> >> +                                   ((uint64_t)bitmap_hi << 32) | 
> >> bitmap_lo);
> >> +    }
> >>
> >>     return FFA_RET_NOT_SUPPORTED;
> >> }
> >> diff --git a/xen/arch/arm/tee/ffa_private.h 
> >> b/xen/arch/arm/tee/ffa_private.h
> >> index 78a0a9815d56..923a071a9d7c 100644
> >> --- a/xen/arch/arm/tee/ffa_private.h
> >> +++ b/xen/arch/arm/tee/ffa_private.h
> >> @@ -340,20 +340,18 @@ struct ffa_ctx_notif {
> >>     uint64_t vm_pending;
> >>
> >>     /*
> >> -     * Source endpoint bound to each VM notification ID (0 means unbound).
> >> +     * Tracks whether an NPI has been raised for local pending 
> >> notifications.
> >> +     * Protected by notif_lock.
> >>      */
> >> -    uint16_t vm_bind[FFA_NUM_VM_NOTIF];
> >> +    bool notif_irq_raised;
> >>
> >>     /*
> >> -     * Lock protecting the hypervisor-managed notification state.
> >> +     * Source endpoint bound to each VM notification ID (0 means unbound).
> >>      */
> >> -    spinlock_t notif_lock;
> >> +    uint16_t vm_bind[FFA_NUM_VM_NOTIF];
> >>
> >> -    /*
> >> -     * Tracks whether a local notification pending interrupt was raised.
> >> -     * Protected by notif_lock.
> >> -     */
> >> -    bool notif_irq_raised;
> >> +    /* Lock protecting local notification state. */
> >> +    spinlock_t notif_lock;
> >>
> >>     /*
> >>      * Bitmap of pending hypervisor notifications (for HYP bitmap queries).
> >> @@ -495,6 +493,7 @@ void ffa_notif_init(void);
> >> void ffa_notif_init_interrupt(void);
> >> int ffa_notif_domain_init(struct domain *d);
> >> void ffa_notif_domain_destroy(struct domain *d);
> >> +bool ffa_notif_fw_enabled(void);
> >>
> >> int32_t ffa_handle_notification_bind(struct cpu_user_regs *regs);
> >> int32_t ffa_handle_notification_unbind(struct cpu_user_regs *regs);
> >> --
> >> 2.53.0
> >>
>