Subject: RE: [PATCH V1 mlx5-next 11/13] vfio/mlx5: Implement vfio_pci driver for mlx5 devices

From: Shameerali Kolothum Thodi <[email-masked]>
Date: Tue, 19 Oct 2021 11:26:29 +0000

> -----Original Message-----
> From: Yishai Hadas [mailto:[email-masked]]
> Sent: 19 October 2021 11:30
> To: Shameerali Kolothum Thodi <[email-masked]>;
> [email-masked]; [email-masked]; [email-masked];
> [email-masked]
> Cc: [email-masked]; [email-masked]; [email-masked];
> [email-masked]; [email-masked]; [email-masked];
> [email-masked]; [email-masked]
> Subject: Re: [PATCH V1 mlx5-next 11/13] vfio/mlx5: Implement vfio_pci driver
> for mlx5 devices
> 
> On 10/19/2021 12:59 PM, Shameerali Kolothum Thodi wrote:
> >
> >> -----Original Message-----
> >> From: Yishai Hadas [mailto:[email-masked]]
> >> Sent: 13 October 2021 10:47
> >> To: [email-masked]; [email-masked]; [email-masked];
> >> [email-masked]
> >> Cc: [email-masked]; [email-masked];
> [email-masked];
> >> [email-masked]; [email-masked]; [email-masked];
> >> [email-masked]; [email-masked]; [email-masked]
> >> Subject: [PATCH V1 mlx5-next 11/13] vfio/mlx5: Implement vfio_pci driver
> for
> >> mlx5 devices
> >>
> >> This patch adds support for vfio_pci driver for mlx5 devices.
> >>
> >> It uses vfio_pci_core to register to the VFIO subsystem and then
> >> implements the mlx5 specific logic in the migration area.
> >>
> >> The migration implementation follows the definition from uapi/vfio.h and
> >> uses the mlx5 VF->PF command channel to achieve it.
> >>
> >> This patch implements the suspend/resume flows.
> >>
> >> Signed-off-by: Yishai Hadas <[email-masked]>
> >> Signed-off-by: Leon Romanovsky <[email-masked]>
> >> ---
> >>   MAINTAINERS                    |   6 +
> >>   drivers/vfio/pci/Kconfig       |   3 +
> >>   drivers/vfio/pci/Makefile      |   2 +
> >>   drivers/vfio/pci/mlx5/Kconfig  |  11 +
> >>   drivers/vfio/pci/mlx5/Makefile |   4 +
> >>   drivers/vfio/pci/mlx5/main.c   | 692
> +++++++++++++++++++++++++++++++++
> >>   6 files changed, 718 insertions(+)
> >>   create mode 100644 drivers/vfio/pci/mlx5/Kconfig
> >>   create mode 100644 drivers/vfio/pci/mlx5/Makefile
> >>   create mode 100644 drivers/vfio/pci/mlx5/main.c
> >>
> >> diff --git a/MAINTAINERS b/MAINTAINERS
> >> index abdcbcfef73d..e824bfab4a01 100644
> >> --- a/MAINTAINERS
> >> +++ b/MAINTAINERS
> >> @@ -19699,6 +19699,12 @@ L:	[email-masked]
> >>   S:	Maintained
> >>   F:	drivers/vfio/platform/
> >>
> >> +VFIO MLX5 PCI DRIVER
> >> +M:	Yishai Hadas <[email-masked]>
> >> +L:	[email-masked]
> >> +S:	Maintained
> >> +F:	drivers/vfio/pci/mlx5/
> >> +
> >>   VGA_SWITCHEROO
> >>   R:	Lukas Wunner <[email-masked]>
> >>   S:	Maintained
> >> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
> >> index 860424ccda1b..187b9c259944 100644
> >> --- a/drivers/vfio/pci/Kconfig
> >> +++ b/drivers/vfio/pci/Kconfig
> >> @@ -43,4 +43,7 @@ config VFIO_PCI_IGD
> >>
> >>   	  To enable Intel IGD assignment through vfio-pci, say Y.
> >>   endif
> >> +
> >> +source "drivers/vfio/pci/mlx5/Kconfig"
> >> +
> >>   endif
> >> diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
> >> index 349d68d242b4..ed9d6f2e0555 100644
> >> --- a/drivers/vfio/pci/Makefile
> >> +++ b/drivers/vfio/pci/Makefile
> >> @@ -7,3 +7,5 @@ obj-$(CONFIG_VFIO_PCI_CORE) += vfio-pci-core.o
> >>   vfio-pci-y := vfio_pci.o
> >>   vfio-pci-$(CONFIG_VFIO_PCI_IGD) += vfio_pci_igd.o
> >>   obj-$(CONFIG_VFIO_PCI) += vfio-pci.o
> >> +
> >> +obj-$(CONFIG_MLX5_VFIO_PCI)           += mlx5/
> >> diff --git a/drivers/vfio/pci/mlx5/Kconfig b/drivers/vfio/pci/mlx5/Kconfig
> >> new file mode 100644
> >> index 000000000000..a3ce00add4fe
> >> --- /dev/null
> >> +++ b/drivers/vfio/pci/mlx5/Kconfig
> >> @@ -0,0 +1,11 @@
> >> +# SPDX-License-Identifier: GPL-2.0-only
> >> +config MLX5_VFIO_PCI
> >> +	tristate "VFIO support for MLX5 PCI devices"
> >> +	depends on MLX5_CORE
> >> +	select VFIO_PCI_CORE
> >> +	help
> >> +	  This provides a PCI support for MLX5 devices using the VFIO
> >> +	  framework. The device specific driver supports suspend/resume
> >> +	  of the MLX5 device.
> >> +
> >> +	  If you don't know what to do here, say N.
> >> diff --git a/drivers/vfio/pci/mlx5/Makefile b/drivers/vfio/pci/mlx5/Makefile
> >> new file mode 100644
> >> index 000000000000..689627da7ff5
> >> --- /dev/null
> >> +++ b/drivers/vfio/pci/mlx5/Makefile
> >> @@ -0,0 +1,4 @@
> >> +# SPDX-License-Identifier: GPL-2.0-only
> >> +obj-$(CONFIG_MLX5_VFIO_PCI) += mlx5-vfio-pci.o
> >> +mlx5-vfio-pci-y := main.o cmd.o
> >> +
> >> diff --git a/drivers/vfio/pci/mlx5/main.c b/drivers/vfio/pci/mlx5/main.c
> >> new file mode 100644
> >> index 000000000000..e36302b444a6
> >> --- /dev/null
> >> +++ b/drivers/vfio/pci/mlx5/main.c
> >> @@ -0,0 +1,692 @@
> >> +// SPDX-License-Identifier: GPL-2.0-only
> >> +/*
> >> + * Copyright (c) 2021, NVIDIA CORPORATION & AFFILIATES. All rights
> reserved
> >> + */
> >> +
> >> +#include <linux/device.h>
> >> +#include <linux/eventfd.h>
> >> +#include <linux/file.h>
> >> +#include <linux/interrupt.h>
> >> +#include <linux/iommu.h>
> >> +#include <linux/module.h>
> >> +#include <linux/mutex.h>
> >> +#include <linux/notifier.h>
> >> +#include <linux/pci.h>
> >> +#include <linux/pm_runtime.h>
> >> +#include <linux/types.h>
> >> +#include <linux/uaccess.h>
> >> +#include <linux/vfio.h>
> >> +#include <linux/sched/mm.h>
> >> +#include <linux/vfio_pci_core.h>
> >> +
> >> +#include "cmd.h"
> >> +
> >> +enum {
> >> +	MLX5VF_PCI_FREEZED = 1 << 0,
> >> +};
> >> +
> >> +enum {
> >> +	MLX5VF_REGION_PENDING_BYTES = 1 << 0,
> >> +	MLX5VF_REGION_DATA_SIZE = 1 << 1,
> >> +};
> >> +
> >> +#define MLX5VF_MIG_REGION_DATA_SIZE SZ_128K
> >> +/* Data section offset from migration region */
> >> +#define MLX5VF_MIG_REGION_DATA_OFFSET
> >> \
> >> +	(sizeof(struct vfio_device_migration_info))
> >> +
> >> +#define VFIO_DEVICE_MIGRATION_OFFSET(x)
> >> \
> >> +	(offsetof(struct vfio_device_migration_info, x))
> >> +
> >> +struct mlx5vf_pci_migration_info {
> >> +	u32 vfio_dev_state; /* VFIO_DEVICE_STATE_XXX */
> >> +	u32 dev_state; /* device migration state */
> >> +	u32 region_state; /* Use MLX5VF_REGION_XXX */
> >> +	u16 vhca_id;
> >> +	struct mlx5_vhca_state_data vhca_state_data;
> >> +};
> >> +
> >> +struct mlx5vf_pci_core_device {
> >> +	struct vfio_pci_core_device core_device;
> >> +	u8 migrate_cap:1;
> >> +	/* protect migartion state */
> >> +	struct mutex state_mutex;
> >> +	struct mlx5vf_pci_migration_info vmig;
> >> +};
> >> +
> >> +static int mlx5vf_pci_unquiesce_device(struct mlx5vf_pci_core_device
> >> *mvdev)
> >> +{
> >> +	return mlx5vf_cmd_resume_vhca(mvdev->core_device.pdev,
> >> +				      mvdev->vmig.vhca_id,
> >> +
> >> MLX5_RESUME_VHCA_IN_OP_MOD_RESUME_MASTER);
> >> +}
> >> +
> >> +static int mlx5vf_pci_quiesce_device(struct mlx5vf_pci_core_device
> *mvdev)
> >> +{
> >> +	return mlx5vf_cmd_suspend_vhca(
> >> +		mvdev->core_device.pdev, mvdev->vmig.vhca_id,
> >> +		MLX5_SUSPEND_VHCA_IN_OP_MOD_SUSPEND_MASTER);
> >> +}
> >> +
> >> +static int mlx5vf_pci_unfreeze_device(struct mlx5vf_pci_core_device
> >> *mvdev)
> >> +{
> >> +	int ret;
> >> +
> >> +	ret = mlx5vf_cmd_resume_vhca(mvdev->core_device.pdev,
> >> +				     mvdev->vmig.vhca_id,
> >> +
> >> MLX5_RESUME_VHCA_IN_OP_MOD_RESUME_SLAVE);
> >> +	if (ret)
> >> +		return ret;
> >> +
> >> +	mvdev->vmig.dev_state &= ~MLX5VF_PCI_FREEZED;
> >> +	return 0;
> >> +}
> >> +
> >> +static int mlx5vf_pci_freeze_device(struct mlx5vf_pci_core_device
> *mvdev)
> >> +{
> >> +	int ret;
> >> +
> >> +	ret = mlx5vf_cmd_suspend_vhca(
> >> +		mvdev->core_device.pdev, mvdev->vmig.vhca_id,
> >> +		MLX5_SUSPEND_VHCA_IN_OP_MOD_SUSPEND_SLAVE);
> >> +	if (ret)
> >> +		return ret;
> >> +
> >> +	mvdev->vmig.dev_state |= MLX5VF_PCI_FREEZED;
> >> +	return 0;
> >> +}
> >> +
> >> +static int mlx5vf_pci_save_device_data(struct mlx5vf_pci_core_device
> >> *mvdev)
> >> +{
> >> +	u32 state_size = 0;
> >> +	int ret;
> >> +
> >> +	if (!(mvdev->vmig.dev_state & MLX5VF_PCI_FREEZED))
> >> +		return -EFAULT;
> >> +
> >> +	/* If we already read state no reason to re-read */
> >> +	if (mvdev->vmig.vhca_state_data.state_size)
> >> +		return 0;
> >> +
> >> +	ret = mlx5vf_cmd_query_vhca_migration_state(
> >> +		mvdev->core_device.pdev, mvdev->vmig.vhca_id, &state_size);
> >> +	if (ret)
> >> +		return ret;
> >> +
> >> +	return mlx5vf_cmd_save_vhca_state(mvdev->core_device.pdev,
> >> +					  mvdev->vmig.vhca_id, state_size,
> >> +					  &mvdev->vmig.vhca_state_data);
> >> +}
> >> +
> >> +static int mlx5vf_pci_new_write_window(struct mlx5vf_pci_core_device
> >> *mvdev)
> >> +{
> >> +	struct mlx5_vhca_state_data *state_data =
> >> &mvdev->vmig.vhca_state_data;
> >> +	u32 num_pages_needed;
> >> +	u64 allocated_ready;
> >> +	u32 bytes_needed;
> >> +
> >> +	/* Check how many bytes are available from previous flows */
> >> +	WARN_ON(state_data->num_pages * PAGE_SIZE <
> >> +		state_data->win_start_offset);
> >> +	allocated_ready = (state_data->num_pages * PAGE_SIZE) -
> >> +			  state_data->win_start_offset;
> >> +	WARN_ON(allocated_ready > MLX5VF_MIG_REGION_DATA_SIZE);
> >> +
> >> +	bytes_needed = MLX5VF_MIG_REGION_DATA_SIZE - allocated_ready;
> >> +	if (!bytes_needed)
> >> +		return 0;
> >> +
> >> +	num_pages_needed = DIV_ROUND_UP_ULL(bytes_needed, PAGE_SIZE);
> >> +	return mlx5vf_add_migration_pages(state_data, num_pages_needed);
> >> +}
> >> +
> >> +static ssize_t
> >> +mlx5vf_pci_handle_migration_data_size(struct mlx5vf_pci_core_device
> >> *mvdev,
> >> +				      char __user *buf, bool iswrite)
> >> +{
> >> +	struct mlx5vf_pci_migration_info *vmig = &mvdev->vmig;
> >> +	u64 data_size;
> >> +	int ret;
> >> +
> >> +	if (iswrite) {
> >> +		/* data_size is writable only during resuming state */
> >> +		if (vmig->vfio_dev_state != VFIO_DEVICE_STATE_RESUMING)
> >> +			return -EINVAL;
> >> +
> >> +		ret = copy_from_user(&data_size, buf, sizeof(data_size));
> >> +		if (ret)
> >> +			return -EFAULT;
> >> +
> >> +		vmig->vhca_state_data.state_size += data_size;
> >> +		vmig->vhca_state_data.win_start_offset += data_size;
> >> +		ret = mlx5vf_pci_new_write_window(mvdev);
> >> +		if (ret)
> >> +			return ret;
> >> +
> >> +	} else {
> >> +		if (vmig->vfio_dev_state != VFIO_DEVICE_STATE_SAVING)
> >> +			return -EINVAL;
> >> +
> >> +		data_size = min_t(u64, MLX5VF_MIG_REGION_DATA_SIZE,
> >> +				  vmig->vhca_state_data.state_size -
> >> +				  vmig->vhca_state_data.win_start_offset);
> >> +		ret = copy_to_user(buf, &data_size, sizeof(data_size));
> >> +		if (ret)
> >> +			return -EFAULT;
> >> +	}
> >> +
> >> +	vmig->region_state |= MLX5VF_REGION_DATA_SIZE;
> >> +	return sizeof(data_size);
> >> +}
> >> +
> >> +static ssize_t
> >> +mlx5vf_pci_handle_migration_data_offset(struct mlx5vf_pci_core_device
> >> *mvdev,
> >> +					char __user *buf, bool iswrite)
> >> +{
> >> +	static const u64 data_offset = MLX5VF_MIG_REGION_DATA_OFFSET;
> >> +	int ret;
> >> +
> >> +	/* RO field */
> >> +	if (iswrite)
> >> +		return -EFAULT;
> >> +
> >> +	ret = copy_to_user(buf, &data_offset, sizeof(data_offset));
> >> +	if (ret)
> >> +		return -EFAULT;
> >> +
> >> +	return sizeof(data_offset);
> >> +}
> >> +
> >> +static ssize_t
> >> +mlx5vf_pci_handle_migration_pending_bytes(struct
> mlx5vf_pci_core_device
> >> *mvdev,
> >> +					  char __user *buf, bool iswrite)
> >> +{
> >> +	struct mlx5vf_pci_migration_info *vmig = &mvdev->vmig;
> >> +	u64 pending_bytes;
> >> +	int ret;
> >> +
> >> +	/* RO field */
> >> +	if (iswrite)
> >> +		return -EFAULT;
> >> +
> >> +	if (vmig->vfio_dev_state == (VFIO_DEVICE_STATE_SAVING |
> >> +				     VFIO_DEVICE_STATE_RUNNING)) {
> >> +		/* In pre-copy state we have no data to return for now,
> >> +		 * return 0 pending bytes
> >> +		 */
> >> +		pending_bytes = 0;
> >> +	} else {
> >> +		if (!vmig->vhca_state_data.state_size)
> >> +			return 0;
> >> +		pending_bytes = vmig->vhca_state_data.state_size -
> >> +				vmig->vhca_state_data.win_start_offset;
> >> +	}
> >> +
> >> +	ret = copy_to_user(buf, &pending_bytes, sizeof(pending_bytes));
> >> +	if (ret)
> >> +		return -EFAULT;
> >> +
> >> +	/* Window moves forward once data from previous iteration was read */
> >> +	if (vmig->region_state & MLX5VF_REGION_DATA_SIZE)
> >> +		vmig->vhca_state_data.win_start_offset +=
> >> +			min_t(u64, MLX5VF_MIG_REGION_DATA_SIZE, pending_bytes);
> >> +
> >> +	WARN_ON(vmig->vhca_state_data.win_start_offset >
> >> +		vmig->vhca_state_data.state_size);
> >> +
> >> +	/* New iteration started */
> >> +	vmig->region_state = MLX5VF_REGION_PENDING_BYTES;
> >> +	return sizeof(pending_bytes);
> >> +}
> >> +
> >> +static int mlx5vf_load_state(struct mlx5vf_pci_core_device *mvdev)
> >> +{
> >> +	if (!mvdev->vmig.vhca_state_data.state_size)
> >> +		return 0;
> >> +
> >> +	return mlx5vf_cmd_load_vhca_state(mvdev->core_device.pdev,
> >> +					  mvdev->vmig.vhca_id,
> >> +					  &mvdev->vmig.vhca_state_data);
> >> +}
> >> +
> >> +static void mlx5vf_reset_mig_state(struct mlx5vf_pci_core_device
> *mvdev)
> >> +{
> >> +	struct mlx5vf_pci_migration_info *vmig = &mvdev->vmig;
> >> +
> >> +	vmig->region_state = 0;
> >> +	mlx5vf_reset_vhca_state(&vmig->vhca_state_data);
> >> +}
> >> +
> >> +static int mlx5vf_pci_set_device_state(struct mlx5vf_pci_core_device
> >> *mvdev,
> >> +				       u32 state)
> >> +{
> >> +	struct mlx5vf_pci_migration_info *vmig = &mvdev->vmig;
> >> +	u32 old_state = vmig->vfio_dev_state;
> >> +	int ret = 0;
> >> +
> >> +	if (vfio_is_state_invalid(state) || vfio_is_state_invalid(old_state))
> >> +		return -EINVAL;
> >> +
> >> +	/* Running switches off */
> >> +	if ((old_state & VFIO_DEVICE_STATE_RUNNING) !=
> >> +	    (state & VFIO_DEVICE_STATE_RUNNING) &&
> >> +	    (old_state & VFIO_DEVICE_STATE_RUNNING)) {
> >> +		ret = mlx5vf_pci_quiesce_device(mvdev);
> >> +		if (ret)
> >> +			return ret;
> >> +		ret = mlx5vf_pci_freeze_device(mvdev);
> >> +		if (ret) {
> >> +			vmig->vfio_dev_state = VFIO_DEVICE_STATE_INVALID;
> >> +			return ret;
> >> +		}
> >> +	}
> >> +
> >> +	/* Resuming switches off */
> >> +	if ((old_state & VFIO_DEVICE_STATE_RESUMING) !=
> >> +	    (state & VFIO_DEVICE_STATE_RESUMING) &&
> >> +	    (old_state & VFIO_DEVICE_STATE_RESUMING)) {
> >> +		/* deserialize state into the device */
> >> +		ret = mlx5vf_load_state(mvdev);
> >> +		if (ret) {
> >> +			vmig->vfio_dev_state = VFIO_DEVICE_STATE_INVALID;
> >> +			return ret;
> >> +		}
> >> +	}
> >> +
> >> +	/* Resuming switches on */
> >> +	if ((old_state & VFIO_DEVICE_STATE_RESUMING) !=
> >> +	    (state & VFIO_DEVICE_STATE_RESUMING) &&
> >> +	    (state & VFIO_DEVICE_STATE_RESUMING)) {
> >> +		mlx5vf_reset_mig_state(mvdev);
> >> +		ret = mlx5vf_pci_new_write_window(mvdev);
> >> +		if (ret)
> >> +			return ret;
> >> +	}
> >> +
> >> +	/* Saving switches on */
> >> +	if ((old_state & VFIO_DEVICE_STATE_SAVING) !=
> >> +	    (state & VFIO_DEVICE_STATE_SAVING) &&
> >> +	    (state & VFIO_DEVICE_STATE_SAVING)) {
> >> +		if (!(state & VFIO_DEVICE_STATE_RUNNING)) {
> >> +			/* serialize post copy */
> >> +			ret = mlx5vf_pci_save_device_data(mvdev);
> > Does it actually get into post-copy here? The pre-copy state(old_state)
> > has the _SAVING bit set already and post-copy state( new state) also
> > has _SAVING set. It looks like we need to handle the post copy in the above
> > "Running switches off" and check for (state & _SAVING).
> >
> > Or Am I missing something?
> >
> 
> The above checks for a change in the SAVING bit, if it was turned on and
> we are not RUNNING it means post copy.
> 
> Turning on SAVING when we are RUNNING will end-up with returning zero
> bytes upon pending bytes as we don't support for now dirty pages.
> 
> see mlx5vf_pci_handle_migration_pending_bytes().

So what you are saying is Qemu won't set a pre-copy state prior to post copy here.
IIRC, that was not the case in our setup and Qemu does set the state to pre-copy
(_RUNNING | _SAVING) , reads the pending_bytes and then set it to post copy
(_SAVING). 

Thanks,
Shameer

> Yishai