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Tue, 25 Nov 2025 15:38:54 +0000 (UTC) X-Farcaster-Flow-ID: 0a0762f7-c031-4a41-9d20-cdfa9e286805 Received: from EX19D012EUA002.ant.amazon.com (10.252.50.32) by EX19MTAEUA002.ant.amazon.com (10.252.50.126) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.29; Tue, 25 Nov 2025 15:38:54 +0000 Received: from EX19D012EUA001.ant.amazon.com (10.252.50.122) by EX19D012EUA002.ant.amazon.com (10.252.50.32) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.29; Tue, 25 Nov 2025 15:38:53 +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 15.02.2562.029; Tue, 25 Nov 2025 15:38:53 +0000 From: "Chalios, Babis" To: "richardcochran@gmail.com" , "dwmw2@infradead.org" , "andrew+netdev@lunn.ch" , "davem@davemloft.net" , "edumazet@google.com" , "kuba@kernel.org" , "pabeni@redhat.com" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" CC: "Chalios, Babis" , "Graf (AWS), Alexander" , "mzxreary@0pointer.de" Subject: [RFC PATCH 2/2] ptp: vmclock: support device notifications Thread-Topic: [RFC PATCH 2/2] ptp: vmclock: support device notifications Thread-Index: AQHcXiGaXBXgjv2OV0ypWqKuhz60Pw== Date: Tue, 25 Nov 2025 15:38:53 +0000 Message-ID: <20251125153830.11487-3-bchalios@amazon.es> References: <20251125153830.11487-1-bchalios@amazon.es> In-Reply-To: <20251125153830.11487-1-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: <61206EE014051B41BE587496E77C2D79@amazon.com> 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 VMClock now expects the hypervisor to send a device notification every time the seqcount lock changes to a new (even) value. Moreover, add support for poll() in VMClock as a means to propagate this notification to user space. poll() will notify listeners every time seq_count has changed to a new (even) value since the last time read() (or open()) was called on the device. 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(). Signed-off-by: Babis Chalios --- drivers/ptp/ptp_vmclock.c | 85 ++++++++++++++++++++++++++++++++++++--- 1 file changed, 80 insertions(+), 5 deletions(-) diff --git a/drivers/ptp/ptp_vmclock.c b/drivers/ptp/ptp_vmclock.c index b3a83b03d9c1..efcdcc5c40cf 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; + uint32_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; @@ -379,8 +388,9 @@ static int vmclock_miscdev_mmap(struct file *fp, struct= 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; @@ -402,8 +412,10 @@ 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)) + if (seq =3D=3D le32_to_cpu(st->clk->seq_count)) { + fst->seq =3D seq; break; + } =20 if (ktime_after(ktime_get(), deadline)) return -ETIMEDOUT; @@ -413,10 +425,51 @@ 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; + + poll_wait(fp, &st->disrupt_wait, wait); + + seq =3D le32_to_cpu(st->clk->seq_count); + if (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; + fst->seq =3D le32_to_cpu(st->clk->seq_count); + + 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 +512,16 @@ 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_probe_acpi(struct device *dev, struct vmclock_state *st) { struct acpi_device *adev =3D ACPI_COMPANION(dev); @@ -479,6 +542,14 @@ static int vmclock_probe_acpi(struct device *dev, stru= ct vmclock_state *st) return -ENODEV; } =20 + 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; } =20 @@ -549,6 +620,8 @@ static int vmclock_probe(struct platform_device *pdev) if (ret) return ret; =20 + init_waitqueue_head(&st->disrupt_wait); + /* * If the structure is big enough, it can be mapped to userspace. * Theoretically a guest OS even using larger pages could still @@ -581,6 +654,8 @@ 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) ? ", " : "", --=20 2.34.1