Re: [PATCH v2 11/20] KVM: s390: arm64: Query Available Arm features

[Janosch Frank <frankja@linux.ibm.com>]

On 9/1/26 4:25 PM, Steffen Eiden wrote:
> On Tue, Sep 01, 2026 at 01:44:09PM +0200, Janosch Frank wrote:
>> On 8/31/26 9:46 PM, sashiko-bot@kernel.org wrote:
>>> Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider:
>>> - [Critical] The EX_TABLE entry in the `qaaf` inline assembly incorrectly places the exception fixup label on the non-faulting `lhi` instruction instead of the potentially faulting `.insn` instruction, which will cause unhandled hardware exceptions to panic the kernel.
>>> - [High] `aef_sysfs_init()` unconditionally calls `aef_init_save_area()`, failing to skip it when the AEF facility is not present, causing a crash on older hardware.
>>> - [High] Off-by-two index error when accessing the QAAF registers array in `kvm_qaaf_read_ftr_reg()`, causing KVM to read incorrect memory offsets for all features.
>>> - [High] If QAAF initialization fails, the global capability flag `info.arm_guest_supp` is not cleared, leading KVM to initialize using uninitialized hardware capability data.
>>> --
>>
>> [...]
>>
>>>> diff --git a/arch/s390/kernel/aef.c b/arch/s390/kernel/aef.c
>>>> new file mode 100644
>>>> index 0000000000000..825e2643a8921
>>>> --- /dev/null
>>>> +++ b/arch/s390/kernel/aef.c
>>> [ ... ]
>>>> +static int  __init aef_query_info(void)
>>>> +{
>>>> +	int ret;
>>>> +
>>>> +	if (IS_ENABLED(CONFIG_KVM_S390_ARM64)) {
>>>> +		info.sae_avail = sclp.has_aef;
>>>> +		info.ptff_avail = ptff_query(PTFF_QAGTO) &&
>>>> +				  ptff_query(PTFF_QAGPT);
>>>> +		info.arm_guest_supp = info.sae_avail && info.ptff_avail;
>>>> +	}

Wait, aef_sysfs_init() already early returns if !enabled.
We'll never end up in this function if !enabled.

Generally I'd like to keep it similar to the kernel UV code.
If QAAF is available create the sysfs files and provide qaaf data.

KVM support is separate from the QAAF data.
I'll have a second look tomorrow.