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charset="utf-8" From: "Chalios, Babis" Similar to live migration, loading a VM from some saved state (aka snapshot) is also an event that calls for clock adjustments in the guest. However, guests might want to take more actions as a response to such events, e.g. as discarding UUIDs, resetting network connections, reseeding entropy pools, etc. These are actions that guests don't typically take during live migration, so add a new field in the vmclock_abi called vm_generation_counter which informs the guest about such events. Hypervisor advertises support for vm_generation_counter through the VMCLOCK_FLAG_VM_GEN_COUNTER_PRESENT flag. Users need to check the presence of this bit in vmclock_abi flags field before using this flag. Signed-off-by: Babis Chalios Reviewed-by: David Woodhouse --- include/uapi/linux/vmclock-abi.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/include/uapi/linux/vmclock-abi.h b/include/uapi/linux/vmclock-= abi.h index 2d99b29ac44a..937fe00e4f33 100644 --- a/include/uapi/linux/vmclock-abi.h +++ b/include/uapi/linux/vmclock-abi.h @@ -115,6 +115,12 @@ struct vmclock_abi { * bit again after the update, using the about-to-be-valid fields. */ #define VMCLOCK_FLAG_TIME_MONOTONIC (1 << 7) + /* + * If the VM_GEN_COUNTER_PRESENT flag is set, the hypervisor will + * bump the vm_generation_counter field every time the guest is + * loaded from some save state (restored from a snapshot). + */ +#define VMCLOCK_FLAG_VM_GEN_COUNTER_PRESENT (1 << 8) =20 __u8 pad[2]; __u8 clock_status; @@ -177,6 +183,15 @@ struct vmclock_abi { __le64 time_frac_sec; /* Units of 1/2^64 of a second */ __le64 time_esterror_nanosec; __le64 time_maxerror_nanosec; + + /* + * This field changes to another non-repeating value when the guest + * has been loaded from a snapshot. In addition to handling a + * disruption in time (which will also be signalled through the + * disruption_marker field), a guest may wish to discard UUIDs, + * reset network connections, reseed entropy, etc. + */ + __le64 vm_generation_counter; }; =20 #endif /* __VMCLOCK_ABI_H__ */ --=20 2.34.1 From nobody Tue Dec 16 13:25:12 2025 Received: from fra-out-006.esa.eu-central-1.outbound.mail-perimeter.amazon.com (fra-out-006.esa.eu-central-1.outbound.mail-perimeter.amazon.com [18.197.217.180]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D62E82F6167; Wed, 3 Dec 2025 12:36:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=18.197.217.180 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764765377; cv=none; b=ZHb0GMk+xW5mLbJR89wWi+URD6gs7SxDVyS1XBh+G/pkB4rQwx11Q3lX7sPb7X3tlq/uTD9Zyqgi0MC2b5DSLX5+OzcNuZjJ2Xf7YEYurZ/NN+SHgtT49lrvJ/BttLI/DePx2A/KW+cFAd8amzMCcGlSVSdI39Ig5RLO/5uPIP4= ARC-Message-Signature: i=1; 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03 Dec 2025 12:36:05 +0000 Received: from EX19MTAEUC001.ant.amazon.com [54.240.197.225:18723] by smtpin.naws.eu-central-1.prod.farcaster.email.amazon.dev [10.0.46.211:2525] with esmtp (Farcaster) id b8e2a5d2-3d1c-4a11-aac5-fb74088490a8; Wed, 3 Dec 2025 12:36:04 +0000 (UTC) X-Farcaster-Flow-ID: b8e2a5d2-3d1c-4a11-aac5-fb74088490a8 Received: from EX19D012EUA002.ant.amazon.com (10.252.50.32) by EX19MTAEUC001.ant.amazon.com (10.252.51.155) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.29; Wed, 3 Dec 2025 12:36:04 +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; Wed, 3 Dec 2025 12:36:04 +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; Wed, 3 Dec 2025 12:36:04 +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" Subject: [PATCH v3 2/4] ptp: vmclock: support device notifications Thread-Topic: [PATCH v3 2/4] ptp: vmclock: support device notifications Thread-Index: AQHcZFFjBNLeKKlRK0+lr2+N+uX+Ew== Date: Wed, 3 Dec 2025 12:36:04 +0000 Message-ID: <20251203123539.7292-3-bchalios@amazon.es> References: <20251203123539.7292-1-bchalios@amazon.es> In-Reply-To: <20251203123539.7292-1-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: <74B5D662FBE07348A6387C763E263B9D@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 From: "Chalios, Babis" 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..49a17435bd35 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 (!(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) ? 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charset="utf-8" From: David Woodhouse The vmclock device provides a PTP clock source and precise timekeeping across live migration and snapshot/restore operations. The binding has a required memory region containing the vmclock_abi structure and an optional interrupt for clock disruption notifications. The full specification is at https://david.woodhou.se/VMClock.pdf Signed-off-by: David Woodhouse Signed-off-by: Babis Chalios Reviewed-by: Krzysztof Kozlowski --- .../bindings/ptp/amazon,vmclock.yaml | 46 +++++++++++++++++++ 1 file changed, 46 insertions(+) create mode 100644 Documentation/devicetree/bindings/ptp/amazon,vmclock.ya= ml diff --git a/Documentation/devicetree/bindings/ptp/amazon,vmclock.yaml b/Do= cumentation/devicetree/bindings/ptp/amazon,vmclock.yaml new file mode 100644 index 000000000000..b98fee20ce5f --- /dev/null +++ b/Documentation/devicetree/bindings/ptp/amazon,vmclock.yaml @@ -0,0 +1,46 @@ +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) +%YAML 1.2 +--- +$id: http://devicetree.org/schemas/ptp/amazon,vmclock.yaml# +$schema: http://devicetree.org/meta-schemas/core.yaml# + +title: Virtual Machine Clock + +maintainers: + - David Woodhouse + +description: + The vmclock device provides a precise clock source and allows for + accurate timekeeping across live migration and snapshot/restore + operations. 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Wed, 3 Dec 2025 12:36:26 +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; Wed, 3 Dec 2025 12:36:26 +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 v3 4/4] ptp: ptp_vmclock: Add device tree support Thread-Topic: [PATCH v3 4/4] ptp: ptp_vmclock: Add device tree support Thread-Index: AQHcZFFw3kvyjXEKIk25GTIOzzoF6A== Date: Wed, 3 Dec 2025 12:36:26 +0000 Message-ID: <20251203123539.7292-5-bchalios@amazon.es> References: <20251203123539.7292-1-bchalios@amazon.es> In-Reply-To: <20251203123539.7292-1-bchalios@amazon.es> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: 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 Content-Type: text/plain; charset="utf-8" From: David Woodhouse Add device tree support to the ptp_vmclock driver, allowing it to probe via device tree in addition to ACPI. Handle optional interrupt for clock disruption notifications, mirroring the ACPI notification behavior. Signed-off-by: David Woodhouse Signed-off-by: Babis Chalios --- drivers/ptp/ptp_vmclock.c | 69 +++++++++++++++++++++++++++++++++++---- 1 file changed, 63 insertions(+), 6 deletions(-) diff --git a/drivers/ptp/ptp_vmclock.c b/drivers/ptp/ptp_vmclock.c index 49a17435bd35..349582f1ccc3 100644 --- a/drivers/ptp/ptp_vmclock.c +++ b/drivers/ptp/ptp_vmclock.c @@ -14,10 +14,12 @@ #include #include #include +#include #include #include #include #include +#include #include #include =20 @@ -536,7 +538,7 @@ vmclock_acpi_notification_handler(acpi_handle __always_= unused handle, wake_up_interruptible(&st->disrupt_wait); } =20 -static int vmclock_setup_notification(struct device *dev, struct vmclock_s= tate *st) +static int vmclock_setup_acpi_notification(struct device *dev) { struct acpi_device *adev =3D ACPI_COMPANION(dev); acpi_status status; @@ -549,10 +551,6 @@ static int vmclock_setup_notification(struct device *d= ev, struct vmclock_state * if (!adev) return -ENODEV; =20 - /* 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); @@ -587,6 +585,58 @@ static int vmclock_probe_acpi(struct device *dev, stru= ct vmclock_state *st) return 0; } =20 +static irqreturn_t vmclock_of_irq_handler(int __always_unused irq, void *d= ev) +{ + struct device *device =3D dev; + struct vmclock_state *st =3D device->driver_data; + + wake_up_interruptible(&st->disrupt_wait); + return IRQ_HANDLED; +} + +static int vmclock_probe_dt(struct device *dev, struct vmclock_state *st) +{ + struct platform_device *pdev =3D to_platform_device(dev); + struct resource *res; + + res =3D platform_get_resource(pdev, IORESOURCE_MEM, 0); + if (!res) + return -ENODEV; + + st->res =3D *res; + + return 0; +} + +static int vmclock_setup_of_notification(struct device *dev) +{ + struct platform_device *pdev =3D to_platform_device(dev); + int irq; + + irq =3D platform_get_irq(pdev, 0); + if (irq < 0) + return irq; + + return devm_request_irq(dev, irq, vmclock_of_irq_handler, IRQF_SHARED, + "vmclock", dev); +} + +static int vmclock_setup_notification(struct device *dev, + struct vmclock_state *st) +{ + /* The device does not support notifications. Nothing else to do */ + if (!(le64_to_cpu(st->clk->flags) & VMCLOCK_FLAG_NOTIFICATION_PRESENT)) + return 0; + + if (has_acpi_companion(dev)) { + return vmclock_setup_acpi_notification(dev); + } else { + return vmclock_setup_of_notification(dev); + } + +} + + static void vmclock_put_idx(void *data) { struct vmclock_state *st =3D data; @@ -607,7 +657,7 @@ static int vmclock_probe(struct platform_device *pdev) if (has_acpi_companion(dev)) ret =3D vmclock_probe_acpi(dev, st); else - ret =3D -EINVAL; /* Only ACPI for now */ + ret =3D vmclock_probe_dt(dev, st); =20 if (ret) { dev_info(dev, "Failed to obtain physical address: %d\n", ret); @@ -707,11 +757,18 @@ static const struct acpi_device_id vmclock_acpi_ids[]= =3D { }; MODULE_DEVICE_TABLE(acpi, vmclock_acpi_ids); =20 +static const struct of_device_id vmclock_of_ids[] =3D { + { .compatible =3D "amazon,vmclock", }, + { }, +}; +MODULE_DEVICE_TABLE(of, vmclock_of_ids); + static struct platform_driver vmclock_platform_driver =3D { .probe =3D vmclock_probe, .driver =3D { .name =3D "vmclock", .acpi_match_table =3D vmclock_acpi_ids, + .of_match_table =3D vmclock_of_ids, }, }; =20 --=20 2.34.1