Re: [PATCH v4 14/14] tty: gunyah: Add tty console driver for RM Console Services

Greg Kroah-Hartman
2022-09-30T12:17:13Z

On Wed, Sep 28, 2022 at 12:56:33PM -0700, Elliot Berman wrote:
> Gunyah provides a console for each VM using the VM console resource
> manager APIs. This driver allows console data from other
> VMs to be accessed via a TTY device and exports a console device to dump
> Linux's own logs to our console.
>
> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
> ---
> MAINTAINERS | 1 +
> drivers/tty/Kconfig | 8 +
> drivers/tty/Makefile | 1 +
> drivers/tty/gunyah_tty.c | 409 +++++++++++++++++++++++++++++++++++++++
> 4 files changed, 419 insertions(+)
> create mode 100644 drivers/tty/gunyah_tty.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index a0cba618e5f6..e8d4a6d9491a 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -8890,6 +8890,7 @@ F: Documentation/devicetree/bindings/firmware/gunyah-hypervisor.yaml
> F: Documentation/virt/gunyah/
> F: arch/arm64/gunyah/
> F: drivers/mailbox/gunyah-msgq.c
> +F: drivers/tty/gunyah_tty.c
> F: drivers/virt/gunyah/
> F: include/asm-generic/gunyah.h
> F: include/linux/gunyah*.h
> diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
> index cc30ff93e2e4..ff86e977f9ac 100644
> --- a/drivers/tty/Kconfig
> +++ b/drivers/tty/Kconfig
> @@ -380,6 +380,14 @@ config RPMSG_TTY
> To compile this driver as a module, choose M here: the module will be
> called rpmsg_tty.
>
> +config GUNYAH_CONSOLE
> + tristate "Gunyah Consoles"
> + depends on GUNYAH
> + help
> + This enables support for console output using Gunyah's Resource Manager RPC.
> + This is normally used when a secondary VM which does not have exclusive access
> + to a real or virtualized serial device and virtio-console is unavailable.

module name?

> +
> endif # TTY
>
> source "drivers/tty/serdev/Kconfig"
> diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
> index 07aca5184a55..d183fbfd835b 100644
> --- a/drivers/tty/Makefile
> +++ b/drivers/tty/Makefile
> @@ -27,5 +27,6 @@ obj-$(CONFIG_GOLDFISH_TTY) += goldfish.o
> obj-$(CONFIG_MIPS_EJTAG_FDC_TTY) += mips_ejtag_fdc.o
> obj-$(CONFIG_VCC) += vcc.o
> obj-$(CONFIG_RPMSG_TTY) += rpmsg_tty.o
> +obj-$(CONFIG_GUNYAH_CONSOLE) += gunyah_tty.o
>
> obj-y += ipwireless/
> diff --git a/drivers/tty/gunyah_tty.c b/drivers/tty/gunyah_tty.c
> new file mode 100644
> index 000000000000..80a20da11ad0
> --- /dev/null
> +++ b/drivers/tty/gunyah_tty.c
> @@ -0,0 +1,409 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2022 Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +
> +#define pr_fmt(fmt) "gh_rsc_mgr_console: " fmt

You are a driver, use dev_printk() functions, no need for pr_fmt() at
all, right?

> +
> +#include <linux/gunyah_rsc_mgr.h>
> +#include <linux/auxiliary_bus.h>
> +#include <linux/workqueue.h>
> +#include <linux/spinlock.h>
> +#include <linux/tty_flip.h>
> +#include <linux/console.h>
> +#include <linux/module.h>
> +#include <linux/kfifo.h>
> +#include <linux/kref.h>
> +#include <linux/slab.h>
> +#include <linux/tty.h>
> +
> +/*
> + * The Linux TTY code does not support dynamic addition of tty derived devices so we need to know
> + * how many tty devices we might need when space is allocated for the tty device. Since VMs might be
> + * added/removed dynamically, we need to make sure we have enough allocated.

Wrap comments at 80 columns please.

> + */
> +#define RSC_MGR_TTY_ADAPTERS 16

We can have dynamic tty devices, so I don't understand this comment.
What really is the problem here?

> +
> +/* # of payload bytes that can fit in a 1-fragment CONSOLE_WRITE message */
> +#define RM_CONS_WRITE_MSG_SIZE ((1 * (GH_MSGQ_MAX_MSG_SIZE - 8)) - 4)
> +
> +struct rm_cons_port {
> + struct tty_port port;
> + u16 vmid;
> + bool open;

Why do you care if it is open or not?

> + unsigned int index;
> +
> + DECLARE_KFIFO(put_fifo, char, 1024);
> + spinlock_t fifo_lock;
> + struct work_struct put_work;
> +
> + struct rm_cons_data *cons_data;
> +};
> +
> +struct rm_cons_data {
> + struct tty_driver *tty_driver;
> + struct device *dev;
> +
> + spinlock_t ports_lock;
> + struct rm_cons_port *ports[RSC_MGR_TTY_ADAPTERS];
> +
> + struct notifier_block rsc_mgr_notif;
> + struct console console;
> +};
> +
> +static void put_work_fn(struct work_struct *ws)
> +{
> + char buf[RM_CONS_WRITE_MSG_SIZE];
> + int count, ret;
> + struct rm_cons_port *port = container_of(ws, struct rm_cons_port, put_work);
> +
> + while (!kfifo_is_empty(&port->put_fifo)) {
> + count = kfifo_out_spinlocked(&port->put_fifo, buf, sizeof(buf), &port->fifo_lock);
> + if (count <= 0)
> + continue;
> +
> + ret = gh_rm_console_write(port->vmid, buf, count);
> + if (ret) {
> + pr_warn_once("failed to send characters: %d\n", ret);

What will this warning help with?

> + break;

If an error happens, shouldn't you keep trying to send the rest of the
data?

> + }
> + }
> +}
> +
> +static int rsc_mgr_console_notif(struct notifier_block *nb, unsigned long cmd, void *data)
> +{
> + int count, i;
> + struct rm_cons_port *rm_port = NULL;
> + struct tty_port *tty_port = NULL;
> + struct rm_cons_data *cons_data = container_of(nb, struct rm_cons_data, rsc_mgr_notif);
> + const struct gh_rm_notification *notif = data;
> + struct gh_rm_notif_vm_console_chars const * const msg = notif->buff;
> +
> + if (cmd != GH_RM_NOTIF_VM_CONSOLE_CHARS ||
> + notif->size < sizeof(*msg))
> + return NOTIFY_DONE;
> +
> + spin_lock(&cons_data->ports_lock);
> + for (i = 0; i < RSC_MGR_TTY_ADAPTERS; i++) {
> + if (!cons_data->ports[i])
> + continue;
> + if (cons_data->ports[i]->vmid == msg->vmid) {
> + rm_port = cons_data->ports[i];
> + break;
> + }
> + }
> + if (rm_port)
> + tty_port = tty_port_get(&rm_port->port);
> + spin_unlock(&cons_data->ports_lock);
> +
> + if (!rm_port)
> + pr_warn("Received unexpected console characters for VMID %u\n", msg->vmid);
> + if (!tty_port)
> + return NOTIFY_DONE;
> +
> + count = tty_buffer_request_room(tty_port, msg->num_bytes);
> + tty_insert_flip_string(tty_port, msg->bytes, count);
> + tty_flip_buffer_push(tty_port);
> +
> + tty_port_put(tty_port);
> + return NOTIFY_OK;
> +}
> +
> +static ssize_t vmid_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> + struct rm_cons_port *rm_port = dev_get_drvdata(dev);
> +
> + if (rm_port->vmid == GH_VMID_SELF)
> + return sysfs_emit(buf, "self\n");
> +
> + return sysfs_emit(buf, "%u\n", rm_port->vmid);

You didn't document this sysfs file, why not?

And tty drivers should not have random sysfs files, please don't add
this.

> +}
> +
> +static DEVICE_ATTR_RO(vmid);
> +
> +static struct attribute *rsc_mgr_tty_dev_attrs[] = {
> + &dev_attr_vmid.attr,
> + NULL
> +};
> +
> +static const struct attribute_group rsc_mgr_tty_dev_attr_group = {
> + .attrs = rsc_mgr_tty_dev_attrs,
> +};
> +
> +static const struct attribute_group *rsc_mgr_tty_dev_attr_groups[] = {
> + &rsc_mgr_tty_dev_attr_group,
> + NULL
> +};
> +
> +static int rsc_mgr_tty_open(struct tty_struct *tty, struct file *filp)
> +{
> + int ret;
> + struct rm_cons_port *rm_port = dev_get_drvdata(tty->dev);
> +
> + if (!rm_port->open) {

Why are you caring if the port is open already or not?

> + ret = gh_rm_console_open(rm_port->vmid);

Can't this just be called for every open()?

And what happens if this changes right after it is checked?

> + if (ret) {
> + pr_err("Failed to open RM console for vmid %x: %d\n", rm_port->vmid, ret);

dev_err()

> + return ret;
> + }
> + rm_port->open = true;
> + }
> +
> + return tty_port_open(&rm_port->port, tty, filp);
> +}
> +
> +static void rsc_mgr_tty_close(struct tty_struct *tty, struct file *filp)
> +{
> + int ret;
> + struct rm_cons_port *rm_port = dev_get_drvdata(tty->dev);
> +
> + if (rm_port->open) {
> + if (rm_port->vmid != GH_VMID_SELF) {
> + ret = gh_rm_console_close(rm_port->vmid);
> + if (ret)
> + pr_warn("Failed to close RM console for vmid %d: %d\n",
> + rm_port->vmid, ret);
> + }
> + rm_port->open = false;

So if you had multiple open/close this would close the console the first
close call, but not the second?

Are you sure you tested this out properly?

> +
> + tty_port_close(&rm_port->port, tty, filp);
> + }
> +
> +}
> +
> +static int rsc_mgr_tty_write(struct tty_struct *tty, const unsigned char *buf, int count)
> +{
> + struct rm_cons_port *rm_port = dev_get_drvdata(tty->dev);
> + int ret;
> +
> + ret = kfifo_in_spinlocked(&rm_port->put_fifo, buf, count, &rm_port->fifo_lock);
> + if (ret > 0)
> + schedule_work(&rm_port->put_work);

Why not just do the write here? Why is a work queue needed?

> +
> + return ret;
> +}
> +
> +static unsigned int rsc_mgr_mgr_tty_write_room(struct tty_struct *tty)
> +{
> + struct rm_cons_port *rm_port = dev_get_drvdata(tty->dev);
> +
> + return kfifo_avail(&rm_port->put_fifo);
> +}
> +
> +static void rsc_mgr_console_write(struct console *co, const char *buf, unsigned count)
> +{
> + struct rm_cons_port *rm_port = co->data;
> + int ret;
> +
> + ret = kfifo_in_spinlocked(&rm_port->put_fifo, buf, count, &rm_port->fifo_lock);
> + if (ret > 0)
> + schedule_work(&rm_port->put_work);

Same here, why not just send the data now?

> +}
> +
> +static struct tty_driver *rsc_mgr_console_device(struct console *co, int *index)
> +{
> + struct rm_cons_port *rm_port = co->data;
> +
> + *index = rm_port->index;
> + return rm_port->port.tty->driver;

Love the locking :(

> +}
> +
> +static int rsc_mgr_console_setup(struct console *co, char *unused)
> +{
> + int ret;
> + struct rm_cons_port *rm_port = co->data;
> +
> + if (!rm_port->open) {
> + ret = gh_rm_console_open(rm_port->vmid);
> + if (ret) {
> + pr_err("Failed to open RM console for vmid %x: %d\n", rm_port->vmid, ret);
> + return ret;
> + }
> + rm_port->open = true;

Again, don't mess with open/close.

> + }
> +
> + return 0;
> +}
> +
> +static int rsc_mgr_console_exit(struct console *co)
> +{
> + int ret;
> + struct rm_cons_port *rm_port = co->data;
> +
> + if (rm_port->open) {
> + ret = gh_rm_console_close(rm_port->vmid);
> + if (ret) {
> + pr_err("Failed to close RM console for vmid %x: %d\n", rm_port->vmid, ret);
> + return ret;
> + }
> + rm_port->open = false;
> + }
> +
> + return 0;
> +}
> +
> +static const struct tty_operations rsc_mgr_tty_ops = {
> + .open = rsc_mgr_tty_open,
> + .close = rsc_mgr_tty_close,
> + .write = rsc_mgr_tty_write,
> + .write_room = rsc_mgr_mgr_tty_write_room,
> +};
> +
> +static void rsc_mgr_port_destruct(struct tty_port *port)
> +{
> + struct rm_cons_port *rm_port = container_of(port, struct rm_cons_port, port);
> + struct rm_cons_data *cons_data = rm_port->cons_data;
> +
> + spin_lock(&cons_data->ports_lock);
> + WARN_ON(cons_data->ports[rm_port->index] != rm_port);

Does this mean you just crashed the system if something went wrong?

How can this ever happen?

> + cons_data->ports[rm_port->index] = NULL;
> + spin_unlock(&cons_data->ports_lock);
> + kfree(rm_port);
> +}
> +
> +static const struct tty_port_operations rsc_mgr_port_ops = {
> + .destruct = rsc_mgr_port_destruct,
> +};
> +
> +static struct rm_cons_port *rsc_mgr_port_create(struct rm_cons_data *cons_data, u16 vmid)
> +{
> + struct rm_cons_port *rm_port;
> + struct device *ttydev;
> + unsigned int index;
> + int ret;
> +
> + rm_port = kzalloc(sizeof(*rm_port), GFP_KERNEL);
> + rm_port->vmid = vmid;
> + INIT_KFIFO(rm_port->put_fifo);
> + spin_lock_init(&rm_port->fifo_lock);
> + INIT_WORK(&rm_port->put_work, put_work_fn);
> + tty_port_init(&rm_port->port);
> + rm_port->port.ops = &rsc_mgr_port_ops;
> +
> + spin_lock(&cons_data->ports_lock);
> + for (index = 0; index < RSC_MGR_TTY_ADAPTERS; index++) {
> + if (!cons_data->ports[index]) {
> + cons_data->ports[index] = rm_port;
> + rm_port->index = index;
> + break;
> + }
> + }
> + spin_unlock(&cons_data->ports_lock);
> + if (index >= RSC_MGR_TTY_ADAPTERS) {
> + ret = -ENOSPC;
> + goto err_put_port;
> + }
> +
> + ttydev = tty_port_register_device_attr(&rm_port->port, cons_data->tty_driver, index,
> + cons_data->dev, rm_port, rsc_mgr_tty_dev_attr_groups);
> + if (IS_ERR(ttydev)) {
> + ret = PTR_ERR(ttydev);
> + goto err_put_port;
> + }
> +
> + return rm_port;
> +err_put_port:
> + tty_port_put(&rm_port->port);
> + return ERR_PTR(ret);
> +}
> +
> +static int rsc_mgr_console_probe(struct auxiliary_device *auxdev,
> + const struct auxiliary_device_id *aux_dev_id)
> +{
> + struct rm_cons_data *cons_data;
> + struct rm_cons_port *rm_port;
> + int ret;
> + u16 vmid;
> +
> + cons_data = devm_kzalloc(&auxdev->dev, sizeof(*cons_data), GFP_KERNEL);
> + if (!cons_data)
> + return -ENOMEM;
> + dev_set_drvdata(&auxdev->dev, cons_data);
> + cons_data->dev = &auxdev->dev;
> +
> + cons_data->tty_driver = tty_alloc_driver(RSC_MGR_TTY_ADAPTERS,
> + TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV);
> + if (IS_ERR(cons_data->tty_driver))
> + return PTR_ERR(cons_data->tty_driver);
> +
> + cons_data->tty_driver->driver_name = "gh";
> + cons_data->tty_driver->name = "ttyGH";

Where did you pick this name from?

Where is it documented?

> + cons_data->tty_driver->type = TTY_DRIVER_TYPE_SYSTEM;
> + cons_data->tty_driver->init_termios = tty_std_termios;
> + tty_set_operations(cons_data->tty_driver, &rsc_mgr_tty_ops);
> +
> + ret = tty_register_driver(cons_data->tty_driver);
> + if (ret) {
> + dev_err(&auxdev->dev, "Could not register tty driver: %d\n", ret);
> + goto err_put_tty;
> + }
> +
> + spin_lock_init(&cons_data->ports_lock);
> +
> + cons_data->rsc_mgr_notif.notifier_call = rsc_mgr_console_notif;
> + ret = gh_rm_register_notifier(&cons_data->rsc_mgr_notif);
> + if (ret) {
> + dev_err(&auxdev->dev, "Could not register for resource manager notifications: %d\n",
> + ret);
> + goto err_put_tty;
> + }
> +
> + rm_port = rsc_mgr_port_create(cons_data, GH_VMID_SELF);
> + if (IS_ERR(rm_port)) {
> + ret = PTR_ERR(rm_port);
> + dev_err(&auxdev->dev, "Could not create own console: %d\n", ret);
> + goto err_unreg_notif;
> + }
> +
> + strncpy(cons_data->console.name, "ttyGH", sizeof(cons_data->console.name));

Again, where did this name come from?

thanks,

greg k-h