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

Nicholas Piggin
2021-06-14T03:07:26Z

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
>
>
>