netdev - Re: [PATCH v8 vfio 4/7] vfio/pds: Add VFIO live migration support

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Date:   Mon, 10 Apr 2023 16:05:37 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Brett Creeley <brett.creeley@....com>
Cc:     <kvm@...r.kernel.org>, <netdev@...r.kernel.org>, <jgg@...dia.com>,
        <yishaih@...dia.com>, <shameerali.kolothum.thodi@...wei.com>,
        <kevin.tian@...el.com>, <shannon.nelson@....com>,
        <drivers@...sando.io>, <simon.horman@...igine.com>
Subject: Re: [PATCH v8 vfio 4/7] vfio/pds: Add VFIO live migration support

On Tue, 4 Apr 2023 12:01:38 -0700
Brett Creeley <brett.creeley@....com> wrote:
> diff --git a/drivers/vfio/pci/pds/lm.c b/drivers/vfio/pci/pds/lm.c
> new file mode 100644
> index 000000000000..855f5da9b99a
> --- /dev/null
> +++ b/drivers/vfio/pci/pds/lm.c
> @@ -0,0 +1,479 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright(c) 2023 Advanced Micro Devices, Inc. */
> +
> +#include <linux/anon_inodes.h>
> +#include <linux/file.h>
> +#include <linux/fs.h>
> +#include <linux/highmem.h>
> +#include <linux/vfio.h>
> +#include <linux/vfio_pci_core.h>
> +
> +#include "vfio_dev.h"
> +#include "cmds.h"
> +
> +#define PDS_VFIO_LM_FILENAME	"pds_vfio_lm"
> +
> +const char *
> +pds_vfio_lm_state(enum vfio_device_mig_state state)
> +{
> +	switch (state) {
> +	case VFIO_DEVICE_STATE_ERROR:
> +		return "VFIO_DEVICE_STATE_ERROR";
> +	case VFIO_DEVICE_STATE_STOP:
> +		return "VFIO_DEVICE_STATE_STOP";
> +	case VFIO_DEVICE_STATE_RUNNING:
> +		return "VFIO_DEVICE_STATE_RUNNING";
> +	case VFIO_DEVICE_STATE_STOP_COPY:
> +		return "VFIO_DEVICE_STATE_STOP_COPY";
> +	case VFIO_DEVICE_STATE_RESUMING:
> +		return "VFIO_DEVICE_STATE_RESUMING";
> +	case VFIO_DEVICE_STATE_RUNNING_P2P:
> +		return "VFIO_DEVICE_STATE_RUNNING_P2P";
> +	default:
> +		return "VFIO_DEVICE_STATE_INVALID";
> +	}
> +
> +	return "VFIO_DEVICE_STATE_INVALID";

Seems a tad redundant.

> +}
> +
[snip]
> +struct file *
> +pds_vfio_step_device_state_locked(struct pds_vfio_pci_device *pds_vfio,
> +				  enum vfio_device_mig_state next)
> +{
> +	enum vfio_device_mig_state cur = pds_vfio->state;
> +	struct device *dev = &pds_vfio->pdev->dev;
> +	int err = 0;
> +
> +	dev_dbg(dev, "%s => %s\n",
> +		pds_vfio_lm_state(cur), pds_vfio_lm_state(next));
> +
> +	if (cur == VFIO_DEVICE_STATE_STOP && next == VFIO_DEVICE_STATE_STOP_COPY) {
> +		/* Device is already stopped
> +		 * create save device data file & get device state from firmware
> +		 */

Standard multi-line comment style please, we're not under net/ here.

> +		err = pds_vfio_get_save_file(pds_vfio);
> +		if (err)
> +			return ERR_PTR(err);
> +
> +		/* Get device state */
> +		err = pds_vfio_get_lm_state_cmd(pds_vfio);
> +		if (err) {
> +			pds_vfio_put_save_file(pds_vfio);
> +			return ERR_PTR(err);
> +		}
> +
> +		return pds_vfio->save_file->filep;
> +	}
> +
> +	if (cur == VFIO_DEVICE_STATE_STOP_COPY && next == VFIO_DEVICE_STATE_STOP) {
> +		/* Device is already stopped
> +		 * delete the save device state file
> +		 */
> +		pds_vfio_put_save_file(pds_vfio);
> +		pds_vfio_send_host_vf_lm_status_cmd(pds_vfio,
> +						    PDS_LM_STA_NONE);
> +		return NULL;
> +	}
> +
> +	if (cur == VFIO_DEVICE_STATE_STOP && next == VFIO_DEVICE_STATE_RESUMING) {
> +		/* create resume device data file */
> +		err = pds_vfio_get_restore_file(pds_vfio);
> +		if (err)
> +			return ERR_PTR(err);
> +
> +		return pds_vfio->restore_file->filep;
> +	}
> +
> +	if (cur == VFIO_DEVICE_STATE_RESUMING && next == VFIO_DEVICE_STATE_STOP) {
> +		/* Set device state */
> +		err = pds_vfio_set_lm_state_cmd(pds_vfio);
> +		if (err)
> +			return ERR_PTR(err);
> +
> +		/* delete resume device data file */
> +		pds_vfio_put_restore_file(pds_vfio);
> +		return NULL;
> +	}
> +
> +	if (cur == VFIO_DEVICE_STATE_RUNNING && next == VFIO_DEVICE_STATE_RUNNING_P2P) {
> +		pds_vfio_send_host_vf_lm_status_cmd(pds_vfio, PDS_LM_STA_IN_PROGRESS);
> +		/* Device should be stopped
> +		 * no interrupts, dma or change in internal state
> +		 */
> +		err = pds_vfio_suspend_device_cmd(pds_vfio);
> +		if (err)
> +			return ERR_PTR(err);
> +
> +		return NULL;
> +	}

The comment here, as well as the no-op transitions from STOP->P2P and
P2P->STOP has me concerned whether a device in this suspend state
really meets the definition of our P2P state.  The RUNNING_P2P state is
a quiescent state where the device must accept access, including
peer-to-peer DMA, but it cannot initiate DMA or interrupts.  Is that
consistent with this suspend state?  Thanks,

Alex

> +
> +	if (cur == VFIO_DEVICE_STATE_RUNNING_P2P && next == VFIO_DEVICE_STATE_RUNNING) {
> +		/* Device should be functional
> +		 * interrupts, dma, mmio or changes to internal state is allowed
> +		 */
> +		err = pds_vfio_resume_device_cmd(pds_vfio);
> +		if (err)
> +			return ERR_PTR(err);
> +
> +		pds_vfio_send_host_vf_lm_status_cmd(pds_vfio,
> +						    PDS_LM_STA_NONE);
> +		return NULL;
> +	}
> +
> +	if (cur == VFIO_DEVICE_STATE_STOP && next == VFIO_DEVICE_STATE_RUNNING_P2P)
> +		return NULL;
> +
> +	if (cur == VFIO_DEVICE_STATE_RUNNING_P2P && next == VFIO_DEVICE_STATE_STOP)
> +		return NULL;
> +
> +	return ERR_PTR(-EINVAL);
> +}