Re: [PATCH v5 13/17] powerpc/pseries/vas: Setup IRQ and fault handling

[Nicholas Piggin <npiggin@gmail.com>]

Excerpts from Haren Myneni's message of June 13, 2021 9:02 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@linux.ibm.com>
> ---
>  arch/powerpc/platforms/pseries/vas.c | 108 +++++++++++++++++++++++++++
>  1 file changed, 108 insertions(+)
> 
> diff --git a/arch/powerpc/platforms/pseries/vas.c b/arch/powerpc/platforms/pseries/vas.c
> index fe375f7a7029..55185bdd3776 100644
> --- a/arch/powerpc/platforms/pseries/vas.c
> +++ b/arch/powerpc/platforms/pseries/vas.c
> @@ -11,6 +11,7 @@
>  #include <linux/types.h>
>  #include <linux/delay.h>
>  #include <linux/slab.h>
> +#include <linux/interrupt.h>
>  #include <asm/machdep.h>
>  #include <asm/hvcall.h>
>  #include <asm/plpar_wrappers.h>
> @@ -190,6 +191,58 @@ int h_query_vas_capabilities(const u64 hcall, u8 query_type, u64 result)
>  }
>  EXPORT_SYMBOL_GPL(h_query_vas_capabilities);
>  
> +/*
> + * hcall to get fault CRB from pHyp.
> + */
> +static int h_get_nx_fault(u32 winid, u64 buffer)
> +{
> +	long 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_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): Failed with error %ld for window(%u)\n",
> +		       H_GET_NX_FAULT, rc, winid);
> +		return -EIO;

3 error messages have 3 different formats for window ID.

I agree with Michael you could just have one error message that reports 
the return value. Also "H_GET_NX_FAULT: " would be nicer than "HCALL(380): "

Check how some other hcall failures are reported, "hcall failed: 
H_CALL_NAME" seems to have a few takers.

> +	}
> +}
> +
> +/*
> + * 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 pseries_vas_window *txwin = data;
> +	struct coprocessor_request_block crb;
> +	struct vas_user_win_ref *tsk_ref;
> +	int rc;
> +
> +	rc = h_get_nx_fault(txwin->vas_win.winid, (u64)virt_to_phys(&crb));
> +	if (!rc) {
> +		tsk_ref = &txwin->vas_win.task_ref;
> +		vas_dump_crb(&crb);
> +		vas_update_csb(&crb, tsk_ref);
> +	}
> +
> +	return IRQ_HANDLED;
> +}
> +
>  /*
>   * Allocate window and setup IRQ mapping.
>   */
> @@ -201,10 +254,51 @@ static int allocate_setup_window(struct pseries_vas_window *txwin,
>  	rc = h_allocate_vas_window(txwin, domain, wintype, DEF_WIN_CREDS);
>  	if (rc)
>  		return rc;
> +	/*
> +	 * On powerVM, pHyp setup and forwards the fault interrupt per

           The hypervisor forwards the fault interrupt per-window...

> +	 * window. So the IRQ setup and fault handling will be done for
> +	 * each open window separately.
> +	 */
> +	txwin->fault_virq = irq_create_mapping(NULL, txwin->fault_irq);
> +	if (!txwin->fault_virq) {
> +		pr_err("Failed irq mapping %d\n", txwin->fault_irq);
> +		rc = -EINVAL;
> +		goto out_win;
> +	}
> +
> +	txwin->name = kasprintf(GFP_KERNEL, "vas-win-%d",
> +				txwin->vas_win.winid);
> +	if (!txwin->name) {
> +		rc = -ENOMEM;
> +		goto out_irq;
> +	}
> +
> +	rc = request_threaded_irq(txwin->fault_virq, NULL,
> +				  pseries_vas_fault_thread_fn, IRQF_ONESHOT,
> +				  txwin->name, txwin);
> +	if (rc) {
> +		pr_err("VAS-Window[%d]: Request IRQ(%u) failed with %d\n",
> +		       txwin->vas_win.winid, txwin->fault_virq, rc);
> +		goto out_free;
> +	}
>  
>  	txwin->vas_win.wcreds_max = DEF_WIN_CREDS;
>  
>  	return 0;
> +out_free:
> +	kfree(txwin->name);
> +out_irq:
> +	irq_dispose_mapping(txwin->fault_virq);
> +out_win:
> +	h_deallocate_vas_window(txwin->vas_win.winid);
> +	return rc;
> +}
> +
> +static inline void free_irq_setup(struct pseries_vas_window *txwin)
> +{
> +	free_irq(txwin->fault_virq, txwin);
> +	irq_dispose_mapping(txwin->fault_virq);
> +	kfree(txwin->name);

Nit, but this freeing is in a different order than the error handling in 
the function does. I'd just keep it the same unless there is a reason to 
be different, in which case it could use a comment.

So long as the irq can't somehow fire and try to use txwin->name, you 
might be okay.

Otherwise I _think_ it's okay, but I don't know the irq APIs well.

Thanks,
Nick

>  }
>  
>  static struct vas_window *vas_allocate_window(struct vas_tx_win_open_attr *uattr,
> @@ -320,6 +414,11 @@ static struct vas_window *vas_allocate_window(struct vas_tx_win_open_attr *uattr
>  	return &txwin->vas_win;
>  
>  out_free:
> +	/*
> +	 * Window is not operational. Free IRQ before closing
> +	 * window so that do not have to hold mutex.
> +	 */

Why don't you have to hold the mutex in that case?

> +	free_irq_setup(txwin);
>  	h_deallocate_vas_window(txwin->vas_win.winid);
>  out:
>  	atomic_dec(&ct_caps->used_lpar_creds);
> @@ -339,7 +438,16 @@ static int deallocate_free_window(struct pseries_vas_window *win)
>  {
>  	int rc = 0;
>  
> +	/*
> +	 * Free IRQ after executing H_DEALLOCATE_VAS_WINDOW HCALL
> +	 * to close the window. pHyp waits for all requests including
> +	 * faults are processed before closing the window - Means all
> +	 * credits are returned. In the case of fault request, credit
> +	 * is returned after OS issues H_GET_NX_FAULT HCALL.
> +	 */
>  	rc = h_deallocate_vas_window(win->vas_win.winid);
> +	if (!rc)
> +		free_irq_setup(win);
>  
>  	return rc;
>  }
> -- 
> 2.18.2
> 
> 
>