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Thu, 18 Dec 2025 14:24:41 +0000 (UTC) X-Farcaster-Flow-ID: 38b9f7c4-1405-49fe-8164-21a6b99d6ff7 Received: from EX19D012EUA003.ant.amazon.com (10.252.50.98) by EX19MTAEUA001.ant.amazon.com (10.252.50.223) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.29; Thu, 18 Dec 2025 14:24:33 +0000 Received: from EX19D012EUA001.ant.amazon.com (10.252.50.122) by EX19D012EUA003.ant.amazon.com (10.252.50.98) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.35; Thu, 18 Dec 2025 14:24:32 +0000 Received: from EX19D012EUA001.ant.amazon.com ([fe80::b7ea:84f7:2c4b:2719]) by EX19D012EUA001.ant.amazon.com ([fe80::b7ea:84f7:2c4b:2719%3]) with mapi id 15.02.2562.035; Thu, 18 Dec 2025 14:24:32 +0000 From: "Chalios, Babis" To: "robh@kernel.org" , "krzk+dt@kernel.org" , "conor+dt@kernel.org" , "richardcochran@gmail.com" , "dwmw2@infradead.org" , "andrew+netdev@lunn.ch" , "davem@davemloft.net" , "edumazet@google.com" , "kuba@kernel.org" , "pabeni@redhat.com" CC: "devicetree@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Chalios, Babis" , "Graf (AWS), Alexander" , "mzxreary@0pointer.de" , "Cali, Marco" , "Woodhouse, David" Subject: [PATCH v4 2/7] ptp: vmclock: support device notifications Thread-Topic: [PATCH v4 2/7] ptp: vmclock: support device notifications Thread-Index: AQHccCoHKiqhmMqx2kixR300dKT0fQ== Date: Thu, 18 Dec 2025 14:24:32 +0000 Message-ID: <20251218142408.8395-3-bchalios@amazon.es> References: <20251218142408.8395-1-bchalios@amazon.es> In-Reply-To: <20251218142408.8395-1-bchalios@amazon.es> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: Content-Type: text/plain; charset="utf-8" Content-ID: Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Add optional support for device notifications in VMClock. When supported, the hypervisor will send a device notification every time it updates the seq_count to a new even value. Moreover, add support for poll() in VMClock as a means to propagate this notification to user space. poll() will return a POLLIN event to listeners every time seq_count changes to a value different than the one last seen (since open() or last read()/pread()). This means that when poll() returns a POLLIN event, listeners need to use read() to observe what has changed and update the reader's view of seq_count. In other words, after a poll() returned, all subsequent calls to poll() will immediately return with a POLLIN event until the listener calls read(). The device advertises support for the notification mechanism by setting flag VMCLOCK_FLAG_NOTIFICATION_PRESENT in vmclock_abi flags field. If the flag is not present the driver won't setup the ACPI notification handler and poll() will always immediately return POLLHUP. Signed-off-by: Babis Chalios Reviewed-by: David Woodhouse --- drivers/ptp/ptp_vmclock.c | 126 +++++++++++++++++++++++++++++-- include/uapi/linux/vmclock-abi.h | 5 ++ 2 files changed, 124 insertions(+), 7 deletions(-) diff --git a/drivers/ptp/ptp_vmclock.c b/drivers/ptp/ptp_vmclock.c index b3a83b03d9c1..a203386c4b09 100644 --- a/drivers/ptp/ptp_vmclock.c +++ b/drivers/ptp/ptp_vmclock.c @@ -5,6 +5,9 @@ * Copyright =C2=A9 2024 Amazon.com, Inc. or its affiliates. */ =20 +#include "linux/poll.h" +#include "linux/types.h" +#include "linux/wait.h" #include #include #include @@ -39,6 +42,7 @@ struct vmclock_state { struct resource res; struct vmclock_abi *clk; struct miscdevice miscdev; + wait_queue_head_t disrupt_wait; struct ptp_clock_info ptp_clock_info; struct ptp_clock *ptp_clock; enum clocksource_ids cs_id, sys_cs_id; @@ -357,10 +361,15 @@ static struct ptp_clock *vmclock_ptp_register(struct = device *dev, return ptp_clock_register(&st->ptp_clock_info, dev); } =20 +struct vmclock_file_state { + struct vmclock_state *st; + atomic_t seq; +}; + static int vmclock_miscdev_mmap(struct file *fp, struct vm_area_struct *vm= a) { - struct vmclock_state *st =3D container_of(fp->private_data, - struct vmclock_state, miscdev); + struct vmclock_file_state *fst =3D fp->private_data; + struct vmclock_state *st =3D fst->st; =20 if ((vma->vm_flags & (VM_READ|VM_WRITE)) !=3D VM_READ) return -EROFS; @@ -379,11 +388,12 @@ static int vmclock_miscdev_mmap(struct file *fp, stru= ct vm_area_struct *vma) static ssize_t vmclock_miscdev_read(struct file *fp, char __user *buf, size_t count, loff_t *ppos) { - struct vmclock_state *st =3D container_of(fp->private_data, - struct vmclock_state, miscdev); + struct vmclock_file_state *fst =3D fp->private_data; + struct vmclock_state *st =3D fst->st; + ktime_t deadline =3D ktime_add(ktime_get(), VMCLOCK_MAX_WAIT); size_t max_count; - uint32_t seq; + uint32_t seq, old_seq; =20 if (*ppos >=3D PAGE_SIZE) return 0; @@ -392,6 +402,7 @@ static ssize_t vmclock_miscdev_read(struct file *fp, ch= ar __user *buf, if (count > max_count) count =3D max_count; =20 + old_seq =3D atomic_read(&fst->seq); while (1) { seq =3D le32_to_cpu(st->clk->seq_count) & ~1U; /* Pairs with hypervisor wmb */ @@ -402,8 +413,16 @@ static ssize_t vmclock_miscdev_read(struct file *fp, c= har __user *buf, =20 /* Pairs with hypervisor wmb */ virt_rmb(); - if (seq =3D=3D le32_to_cpu(st->clk->seq_count)) - break; + if (seq =3D=3D le32_to_cpu(st->clk->seq_count)) { + /* + * Either we updated fst->seq to seq (the latest version we observed) + * or someone else did (old_seq =3D=3D seq), so we can break. + */ + if (atomic_try_cmpxchg(&fst->seq, &old_seq, seq) || + old_seq =3D=3D seq) { + break; + } + } =20 if (ktime_after(ktime_get(), deadline)) return -ETIMEDOUT; @@ -413,10 +432,58 @@ static ssize_t vmclock_miscdev_read(struct file *fp, = char __user *buf, return count; } =20 +static __poll_t vmclock_miscdev_poll(struct file *fp, poll_table *wait) +{ + struct vmclock_file_state *fst =3D fp->private_data; + struct vmclock_state *st =3D fst->st; + uint32_t seq; + + /* + * Hypervisor will not send us any notifications, so fail immediately + * to avoid having caller sleeping for ever. + */ + if (!(le64_to_cpu(st->clk->flags) & VMCLOCK_FLAG_NOTIFICATION_PRESENT)) + return POLLHUP; + + poll_wait(fp, &st->disrupt_wait, wait); + + seq =3D le32_to_cpu(st->clk->seq_count); + if (atomic_read(&fst->seq) !=3D seq) + return POLLIN | POLLRDNORM; + + return 0; +} + +static int vmclock_miscdev_open(struct inode *inode, struct file *fp) +{ + struct vmclock_state *st =3D container_of(fp->private_data, + struct vmclock_state, miscdev); + struct vmclock_file_state *fst =3D kzalloc(sizeof(*fst), GFP_KERNEL); + + if (!fst) + return -ENOMEM; + + fst->st =3D st; + atomic_set(&fst->seq, 0); + + fp->private_data =3D fst; + + return 0; +} + +static int vmclock_miscdev_release(struct inode *inode, struct file *fp) +{ + kfree(fp->private_data); + return 0; +} + static const struct file_operations vmclock_miscdev_fops =3D { .owner =3D THIS_MODULE, + .open =3D vmclock_miscdev_open, + .release =3D vmclock_miscdev_release, .mmap =3D vmclock_miscdev_mmap, .read =3D vmclock_miscdev_read, + .poll =3D vmclock_miscdev_poll, }; =20 /* module operations */ @@ -459,6 +526,44 @@ static acpi_status vmclock_acpi_resources(struct acpi_= resource *ares, void *data return AE_ERROR; } =20 +static void +vmclock_acpi_notification_handler(acpi_handle __always_unused handle, + u32 __always_unused event, void *dev) +{ + struct device *device =3D dev; + struct vmclock_state *st =3D device->driver_data; + + wake_up_interruptible(&st->disrupt_wait); +} + +static int vmclock_setup_notification(struct device *dev, struct vmclock_s= tate *st) +{ + struct acpi_device *adev =3D ACPI_COMPANION(dev); + acpi_status status; + + /* + * This should never happen as this function is only called when + * has_acpi_companion(dev) is true, but the logic is sufficiently + * complex that Coverity can't see the tautology. + */ + if (!adev) + return -ENODEV; + + /* The device does not support notifications. Nothing else to do */ + if (!(le64_to_cpu(st->clk->flags) & VMCLOCK_FLAG_NOTIFICATION_PRESENT)) + return 0; + + status =3D acpi_install_notify_handler(adev->handle, ACPI_DEVICE_NOTIFY, + vmclock_acpi_notification_handler, + dev); + if (ACPI_FAILURE(status)) { + dev_err(dev, "failed to install notification handler"); + return -ENODEV; + } + + return 0; +} + static int vmclock_probe_acpi(struct device *dev, struct vmclock_state *st) { struct acpi_device *adev =3D ACPI_COMPANION(dev); @@ -549,6 +654,11 @@ static int vmclock_probe(struct platform_device *pdev) if (ret) return ret; =20 + init_waitqueue_head(&st->disrupt_wait); + ret =3D vmclock_setup_notification(dev, st); + if (ret) + return ret; + /* * If the structure is big enough, it can be mapped to userspace. * Theoretically a guest OS even using larger pages could still @@ -581,6 +691,8 @@ static int vmclock_probe(struct platform_device *pdev) return -ENODEV; } =20 + dev->driver_data =3D st; + dev_info(dev, "%s: registered %s%s%s\n", st->name, st->miscdev.minor ? "miscdev" : "", (st->miscdev.minor && st->ptp_clock) ? ", " : "", diff --git a/include/uapi/linux/vmclock-abi.h b/include/uapi/linux/vmclock-= abi.h index 937fe00e4f33..d320623b0118 100644 --- a/include/uapi/linux/vmclock-abi.h +++ b/include/uapi/linux/vmclock-abi.h @@ -121,6 +121,11 @@ struct vmclock_abi { * loaded from some save state (restored from a snapshot). */ #define VMCLOCK_FLAG_VM_GEN_COUNTER_PRESENT (1 << 8) + /* + * If the NOTIFICATION_PRESENT flag is set, the hypervisor will send + * a notification every time it updates seq_count to a new even number. + */ +#define VMCLOCK_FLAG_NOTIFICATION_PRESENT (1 << 9) =20 __u8 pad[2]; __u8 clock_status; --=20 2.34.1