Re: [PATCH v16 00/45] arm64: Support for Arm CCA in KVM

[Alper Gun]

On Tue, Aug 11, 2026 at 8:08 PM Gavin Shan <gshan@xxxxxxxxxx> wrote:
> As the following calltrace indicates, -EAGAIN is returned from tf-rmm::update_ripas()
> because true is returned from s2tte_drain_pending() for the S2TTE corresponding to
> IPA 0x80000000. Linux host received error (RMI_ERROR_RTT, level=3) in ripas_change().
> Upon this specific error and the IPA range [0x80000000 0x90000000], find_map_level()
> returns level of 2, and realm_create_rtt_levels() returns 0 without populating any
> RTTs. After that, rmi_rtt_set_ripas() is re-executed and the above loop starts over
> again.
>
>    Linux host
>    ==========
>    kvm_arch_vcpu_ioctl_run                     // cca/host-v16
>      check_vcpu_requests
>        kvm_check_request
>          kvm_rec_handle_request
>            kvm_complete_ripas_change
>              realm_set_ipa_state
>                ripas_change
>                  rmi_rtt_set_ripas
>                    SMC_RMI_RTT_SET_RIPAS
>
>    TF-RMM
>    ======
>    SMC_RMI_RTT_SET_RIPAS                      // tf-rmm/topics/rmm-v2.0-poc_3
>      smc_rtt_set_ripas
>        s2tt_walk_lock_unlock
>        rtt_set_ripas_range
>          update_ripas
>            s2tte_drain_pending                // true, returns -EAGAIN
>
> The problem is the pending-bit for RTE corresponding IPA address 0x80000000 isn't cleared
> when SMC_RMI_RTT_SET_RIPAS is invoked. I didn't figure out how this bit is set and why
> it's not cleared in time.
>

Hi Gavin, Suzuki,

I think I ran into a similar issue on rmm-v2.0-poc_3 last week.
This looks like a potential RMM bug: could bit 32 be part of the physical
Address (if PA >= 4 GiB)?

It seems s2tte_drain_pending() in lib/s2tt/src/s2tt.c checks bit 32 without
checking whether the descriptor is valid or invalid.

In my testing, guarding the drain checks with a check for S2TTE_INVALID seemed
to resolve the boot hang:
--- a/lib/s2tt/src/s2tt.c
+++ b/lib/s2tt/src/s2tt.c
@@ -1701,6 +1701,10 @@ unsigned long
s2tte_clear_drain_pending(unsigned long s2tte)

 bool s2tte_drain_pending(unsigned long s2tte)
 {
+ if ((s2tte & S2TT_DESC_VALID_MASK) != S2TTE_INVALID) {
+ return false;
+ }
+
  return (s2tte & S2TTE_SW_DRAIN_PENDING_BIT) != 0UL;
 }

@@ -1730,11 +1734,19 @@ unsigned long
s2tte_clear_tlbi_pending(unsigned long s2tte)

 bool s2tte_tlbi_pending(unsigned long s2tte)
 {
+ if ((s2tte & S2TT_DESC_VALID_MASK) != S2TTE_INVALID) {
+ return false;
+ }
+
  return (s2tte & S2TTE_SW_TLBI_PENDING_BIT) != 0UL;
 }

 unsigned int s2tte_drain_handle(unsigned long s2tte)
 {
+ if ((s2tte & S2TT_DESC_VALID_MASK) != S2TTE_INVALID) {
+ return 0U;
+ }
+
  return (unsigned int)EXTRACT(S2TTE_SW_HANDLE, s2tte);
 }

Sharing in case it helps.
Thanks,
Alper