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

[Suzuki K Poulose <suzuki.poulose@arm.com>]

Hi Alper, Gavin

On 12/08/2026 04:25, Alper Gun wrote:
> On Tue, Aug 11, 2026 at 8:08 PM Gavin Shan <gshan@redhat.com> 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.

Thanks for the details.

>>
> 
> 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;

We should use also consider cases where the entry is INVALID, but
has HIPAS=ASSIGNED/ASSIGNED_DEV to make it tighter. So, I think
it is better to use :

s2tte_is_unassigned() or in the library stick to :

if (!s2tte_has_hipas(s2tte, S2TTE_INVALID_HIPAS_UNASSIGNED))
	return false;

May be we should assert this and make the caller responsible for
checking the bit. I will leave it to the tf-RMM team to fix.

But for now, please use the above fix.

Cheers
Suzuki


> + }
> +
>    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