[PATCH v4 12/16] powerpc/pseries/vas: Setup IRQ and fault handling

[Nicholas Piggin]

Excerpts from Haren Myneni's message of May 21, 2021 7:39 pm:
> 
> NX generates an interrupt when sees a fault on the user space
> buffer and the hypervisor forwards that interrupt to OS. Then
> the kernel handles the interrupt by issuing H_GET_NX_FAULT hcall
> to retrieve the fault CRB information.
> 
> This patch also adds changes to setup and free IRQ per each
> window and also handles the fault by updating the CSB.
> 
> Signed-off-by: Haren Myneni <haren at linux.ibm.com>
> ---
>  arch/powerpc/platforms/pseries/vas.c | 111 +++++++++++++++++++++++++++
>  1 file changed, 111 insertions(+)
> 
> diff --git a/arch/powerpc/platforms/pseries/vas.c b/arch/powerpc/platforms/pseries/vas.c
> index ef0c455f6e93..31dc17573f50 100644
> --- a/arch/powerpc/platforms/pseries/vas.c
> +++ b/arch/powerpc/platforms/pseries/vas.c
> @@ -224,6 +224,62 @@ int plpar_vas_query_capabilities(const u64 hcall, u8 query_type,
>  }
>  EXPORT_SYMBOL_GPL(plpar_vas_query_capabilities);
>  
> +/*
> + * HCALL to get fault CRB from pHyp.
> + */
> +static int plpar_get_nx_fault(u32 winid, u64 buffer)
> +{
> +	int64_t rc;
> +
> +	rc = plpar_hcall_norets(H_GET_NX_FAULT, winid, buffer);
> +
> +	switch (rc) {
> +	case H_SUCCESS:
> +		return 0;
> +	case H_PARAMETER:
> +		pr_err("HCALL(%x): Invalid window ID %u\n", H_GET_NX_FAULT,
> +		       winid);
> +		return -EINVAL;
> +	case H_STATE:
> +		pr_err("HCALL(%x): No outstanding faults for window ID %u\n",
> +		       H_GET_NX_FAULT, winid);
> +		return -EINVAL;
> +	case H_PRIVILEGE:
> +		pr_err("HCALL(%x): Window(%u): Invalid fault buffer 0x%llx\n",
> +		       H_GET_NX_FAULT, winid, buffer);
> +		return -EACCES;
> +	default:
> +		pr_err("HCALL(%x): Unexpected error %lld for window(%u)\n",
> +		       H_GET_NX_FAULT, rc, winid);
> +		return -EIO;
> +	}
> +}

Out of curiosity, you get one of these errors and it just drops the
interrupt on the floor. Then what happens, I assume everything
stops. Should it put some error in the csb, or signal the process or
something? Or is there nothing very sane that can be done?

> +
> +/*
> + * Handle the fault interrupt.
> + * When the fault interrupt is received for each window, query pHyp to get
> + * the fault CRB on the specific fault. Then process the CRB by updating
> + * CSB or send signal if the user space CSB is invalid.
> + * Note: pHyp forwards an interrupt for each fault request. So one fault
> + *	CRB to process for each H_GET_NX_FAULT HCALL.
> + */
> +irqreturn_t pseries_vas_fault_thread_fn(int irq, void *data)
> +{
> +	struct vas_window *txwin = data;
> +	struct coprocessor_request_block crb;
> +	struct vas_user_win_ref *tsk_ref;
> +	int rc;
> +
> +	rc = plpar_get_nx_fault(txwin->winid, (u64)virt_to_phys(&crb));
> +	if (!rc) {
> +		tsk_ref = &txwin->task_ref;
> +		vas_dump_crb(&crb);

This (and existing powernv vas code) is printk()ing a lot of lines per 
fault. This should be pretty normal operation I think? It should avoid
filling the kernel logs, if so. Particularly if it can be triggered by 
userspace.

I know it's existing code, so could be fixed separately from the series.


> +		vas_update_csb(&crb, tsk_ref);

> +	}

> +
> +	return IRQ_HANDLED;
> +}
> +