From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5F666C433FF for ; Sat, 3 Aug 2019 11:14:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2803B2075C for ; Sat, 3 Aug 2019 11:14:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564830841; bh=DDOltPrsU1Cyqv7v03ERN+KXqFMSE8LRxVficDjFyvc=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=Oazq2QvCHG0TbICG7WVRH25R3t9CKmCE1KM+qbYNnH/24K3FIuD6el1NxFwdhKzgy rUEuv4ye/MfuiG0CASavWEcFhZR4IzC8mRPNW04RGVMtn7wWV/dpHsY2pErfL57qwV G6TqBiP8q5BcIuWhNjvGuJQzbvpLyN+gVcwNRYxE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389457AbfHCLOA (ORCPT ); Sat, 3 Aug 2019 07:14:00 -0400 Received: from inca-roads.misterjones.org ([213.251.177.50]:36016 "EHLO inca-roads.misterjones.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389332AbfHCLN7 (ORCPT ); Sat, 3 Aug 2019 07:13:59 -0400 Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why) by cheepnis.misterjones.org with esmtpsa (TLSv1.2:AES256-GCM-SHA384:256) (Exim 4.80) (envelope-from ) id 1htrys-00079D-8V; Sat, 03 Aug 2019 13:13:46 +0200 Date: Sat, 3 Aug 2019 12:13:43 +0100 From: Marc Zyngier To: Steven Price Cc: Catalin Marinas , Paolo Bonzini , Radim =?UTF-8?B?S3LEjW3DocWZ?= , Russell King , Will Deacon , James Morse , Julien Thierry , Suzuki K Pouloze , kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, peter.maydell@linaro.org Subject: Re: [PATCH 1/9] KVM: arm64: Document PV-time interface Message-ID: <20190803121343.2f482200@why> In-Reply-To: <20190802145017.42543-2-steven.price@arm.com> References: <20190802145017.42543-1-steven.price@arm.com> <20190802145017.42543-2-steven.price@arm.com> Organization: Approximate X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: steven.price@arm.com, catalin.marinas@arm.com, pbonzini@redhat.com, rkrcmar@redhat.com, linux@armlinux.org.uk, will@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, peter.maydell@linaro.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on cheepnis.misterjones.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2 Aug 2019 15:50:09 +0100 Steven Price wrote: [+Peter for the userspace aspect of things] Hi Steve, > Introduce a paravirtualization interface for KVM/arm64 based on the > "Arm Paravirtualized Time for Arm-Base Systems" specification DEN 0057A. > > This only adds the details about "Stolen Time" as the details of "Live > Physical Time" have not been fully agreed. > > User space can specify a reserved area of memory for the guest and > inform KVM to populate the memory with information on time that the host > kernel has stolen from the guest. > > A hypercall interface is provided for the guest to interrogate the > hypervisor's support for this interface and the location of the shared > memory structures. > > Signed-off-by: Steven Price > --- > Documentation/virtual/kvm/arm/pvtime.txt | 107 +++++++++++++++++++++++ > 1 file changed, 107 insertions(+) > create mode 100644 Documentation/virtual/kvm/arm/pvtime.txt > > diff --git a/Documentation/virtual/kvm/arm/pvtime.txt b/Documentation/virtual/kvm/arm/pvtime.txt > new file mode 100644 > index 000000000000..e6ae9799e1d5 > --- /dev/null > +++ b/Documentation/virtual/kvm/arm/pvtime.txt > @@ -0,0 +1,107 @@ > +Paravirtualized time support for arm64 > +====================================== > + > +Arm specification DEN0057/A defined a standard for paravirtualised time > +support for Aarch64 guests: nit: AArch64 > + > +https://developer.arm.com/docs/den0057/a Between this file and the above document, which one is authoritative? > + > +KVM/Arm64 implements the stolen time part of this specification by providing nit: KVM/arm64 > +some hypervisor service calls to support a paravirtualized guest obtaining a > +view of the amount of time stolen from its execution. > + > +Two new SMCCC compatible hypercalls are defined: > + > +PV_FEATURES 0xC5000020 > +PV_TIME_ST 0xC5000022 > + > +These are only available in the SMC64/HVC64 calling convention as > +paravirtualized time is not available to 32 bit Arm guests. > + > +PV_FEATURES > + Function ID: (uint32) : 0xC5000020 > + PV_func_id: (uint32) : Either PV_TIME_LPT or PV_TIME_ST > + Return value: (int32) : NOT_SUPPORTED (-1) or SUCCESS (0) if the relevant > + PV-time feature is supported by the hypervisor. How is PV_FEATURES discovered? Is the intention to make it a generic ARM-wide PV discovery mechanism, not specific to PV time? > + > +PV_TIME_ST > + Function ID: (uint32) : 0xC5000022 > + Return value: (int64) : IPA of the stolen time data structure for this > + (V)CPU. On failure: > + NOT_SUPPORTED (-1) > + Is the size implicit? What are the memory attributes? This either needs documenting here, or point to the right bit to the spec. > +Stolen Time > +----------- > + > +The structure pointed to by the PV_TIME_ST hypercall is as follows: > + > + Field | Byte Length | Byte Offset | Description > + ----------- | ----------- | ----------- | -------------------------- > + Revision | 4 | 0 | Must be 0 for version 0.1 > + Attributes | 4 | 4 | Must be 0 > + Stolen time | 8 | 8 | Stolen time in unsigned > + | | | nanoseconds indicating how > + | | | much time this VCPU thread > + | | | was involuntarily not > + | | | running on a physical CPU. > + > +The structure will be updated by the hypervisor periodically as time is stolen Is it really periodic? If so, when is the update frequency? > +from the VCPU. It will be present within a reserved region of the normal > +memory given to the guest. The guest should not attempt to write into this > +memory. There is a structure by VCPU of the guest. What if the vcpu writes to it? Does it get a fault? If there is a structure per vcpu, what is the layout in memory? How does a vcpu find its own data structure? Is that the address returned by PV_TIME_ST? > + > +User space interface > +==================== > + > +User space can request that KVM provide the paravirtualized time interface to > +a guest by creating a KVM_DEV_TYPE_ARM_PV_TIME device, for example: > + > + struct kvm_create_device pvtime_device = { > + .type = KVM_DEV_TYPE_ARM_PV_TIME, > + .attr = 0, > + .flags = 0, > + }; > + > + pvtime_fd = ioctl(vm_fd, KVM_CREATE_DEVICE, &pvtime_device); > + > +The guest IPA of the structures must be given to KVM. This is the base address nit: s/guest // > +of an array of stolen time structures (one for each VCPU). For example: > + > + struct kvm_device_attr st_base = { > + .group = KVM_DEV_ARM_PV_TIME_PADDR, > + .attr = KVM_DEV_ARM_PV_TIME_ST, > + .addr = (u64)(unsigned long)&st_paddr > + }; > + > + ioctl(pvtime_fd, KVM_SET_DEVICE_ATTR, &st_base); So the allocation itself is performed by the kernel? What are the ordering requirements between creating vcpus and the device? What are the alignment requirements for the base address? > + > +For migration (or save/restore) of a guest it is necessary to save the contents > +of the shared page(s) and later restore them. KVM_DEV_ARM_PV_TIME_STATE_SIZE > +provides the size of this data and KVM_DEV_ARM_PV_TIME_STATE allows the state > +to be read/written. Is the size variable depending on the number of vcpus? > + > +It is also necessary for the physical address to be set identically when > +restoring. > + > + void *save_state(int fd, u64 attr, u32 *size) { > + struct kvm_device_attr get_size = { > + .group = KVM_DEV_ARM_PV_TIME_STATE_SIZE, > + .attr = attr, > + .addr = (u64)(unsigned long)size > + }; > + > + ioctl(fd, KVM_GET_DEVICE_ATTR, get_size); > + > + void *buffer = malloc(*size); > + > + struct kvm_device_attr get_state = { > + .group = KVM_DEV_ARM_PV_TIME_STATE, > + .attr = attr, > + .addr = (u64)(unsigned long)size > + }; > + > + ioctl(fd, KVM_GET_DEVICE_ATTR, buffer); > + } > + > + void *st_state = save_state(pvtime_fd, KVM_DEV_ARM_PV_TIME_ST, &st_size); > + Thanks, M. -- Without deviation from the norm, progress is not possible. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_2 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 035C9C433FF for ; Sat, 3 Aug 2019 11:14:04 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 8CC232086A for ; Sat, 3 Aug 2019 11:14:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8CC232086A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id E7F134A4EA; 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Sat, 03 Aug 2019 13:13:46 +0200 Date: Sat, 3 Aug 2019 12:13:43 +0100 From: Marc Zyngier To: Steven Price Subject: Re: [PATCH 1/9] KVM: arm64: Document PV-time interface Message-ID: <20190803121343.2f482200@why> In-Reply-To: <20190802145017.42543-2-steven.price@arm.com> References: <20190802145017.42543-1-steven.price@arm.com> <20190802145017.42543-2-steven.price@arm.com> Organization: Approximate X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: steven.price@arm.com, catalin.marinas@arm.com, pbonzini@redhat.com, rkrcmar@redhat.com, linux@armlinux.org.uk, will@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, peter.maydell@linaro.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on cheepnis.misterjones.org); SAEximRunCond expanded to false Cc: kvm@vger.kernel.org, Catalin Marinas , linux-doc@vger.kernel.org, Russell King , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Paolo Bonzini , Will Deacon , kvmarm@lists.cs.columbia.edu X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Fri, 2 Aug 2019 15:50:09 +0100 Steven Price wrote: [+Peter for the userspace aspect of things] Hi Steve, > Introduce a paravirtualization interface for KVM/arm64 based on the > "Arm Paravirtualized Time for Arm-Base Systems" specification DEN 0057A. > > This only adds the details about "Stolen Time" as the details of "Live > Physical Time" have not been fully agreed. > > User space can specify a reserved area of memory for the guest and > inform KVM to populate the memory with information on time that the host > kernel has stolen from the guest. > > A hypercall interface is provided for the guest to interrogate the > hypervisor's support for this interface and the location of the shared > memory structures. > > Signed-off-by: Steven Price > --- > Documentation/virtual/kvm/arm/pvtime.txt | 107 +++++++++++++++++++++++ > 1 file changed, 107 insertions(+) > create mode 100644 Documentation/virtual/kvm/arm/pvtime.txt > > diff --git a/Documentation/virtual/kvm/arm/pvtime.txt b/Documentation/virtual/kvm/arm/pvtime.txt > new file mode 100644 > index 000000000000..e6ae9799e1d5 > --- /dev/null > +++ b/Documentation/virtual/kvm/arm/pvtime.txt > @@ -0,0 +1,107 @@ > +Paravirtualized time support for arm64 > +====================================== > + > +Arm specification DEN0057/A defined a standard for paravirtualised time > +support for Aarch64 guests: nit: AArch64 > + > +https://developer.arm.com/docs/den0057/a Between this file and the above document, which one is authoritative? > + > +KVM/Arm64 implements the stolen time part of this specification by providing nit: KVM/arm64 > +some hypervisor service calls to support a paravirtualized guest obtaining a > +view of the amount of time stolen from its execution. > + > +Two new SMCCC compatible hypercalls are defined: > + > +PV_FEATURES 0xC5000020 > +PV_TIME_ST 0xC5000022 > + > +These are only available in the SMC64/HVC64 calling convention as > +paravirtualized time is not available to 32 bit Arm guests. > + > +PV_FEATURES > + Function ID: (uint32) : 0xC5000020 > + PV_func_id: (uint32) : Either PV_TIME_LPT or PV_TIME_ST > + Return value: (int32) : NOT_SUPPORTED (-1) or SUCCESS (0) if the relevant > + PV-time feature is supported by the hypervisor. How is PV_FEATURES discovered? Is the intention to make it a generic ARM-wide PV discovery mechanism, not specific to PV time? > + > +PV_TIME_ST > + Function ID: (uint32) : 0xC5000022 > + Return value: (int64) : IPA of the stolen time data structure for this > + (V)CPU. On failure: > + NOT_SUPPORTED (-1) > + Is the size implicit? What are the memory attributes? This either needs documenting here, or point to the right bit to the spec. > +Stolen Time > +----------- > + > +The structure pointed to by the PV_TIME_ST hypercall is as follows: > + > + Field | Byte Length | Byte Offset | Description > + ----------- | ----------- | ----------- | -------------------------- > + Revision | 4 | 0 | Must be 0 for version 0.1 > + Attributes | 4 | 4 | Must be 0 > + Stolen time | 8 | 8 | Stolen time in unsigned > + | | | nanoseconds indicating how > + | | | much time this VCPU thread > + | | | was involuntarily not > + | | | running on a physical CPU. > + > +The structure will be updated by the hypervisor periodically as time is stolen Is it really periodic? If so, when is the update frequency? > +from the VCPU. It will be present within a reserved region of the normal > +memory given to the guest. The guest should not attempt to write into this > +memory. There is a structure by VCPU of the guest. What if the vcpu writes to it? Does it get a fault? If there is a structure per vcpu, what is the layout in memory? How does a vcpu find its own data structure? Is that the address returned by PV_TIME_ST? > + > +User space interface > +==================== > + > +User space can request that KVM provide the paravirtualized time interface to > +a guest by creating a KVM_DEV_TYPE_ARM_PV_TIME device, for example: > + > + struct kvm_create_device pvtime_device = { > + .type = KVM_DEV_TYPE_ARM_PV_TIME, > + .attr = 0, > + .flags = 0, > + }; > + > + pvtime_fd = ioctl(vm_fd, KVM_CREATE_DEVICE, &pvtime_device); > + > +The guest IPA of the structures must be given to KVM. This is the base address nit: s/guest // > +of an array of stolen time structures (one for each VCPU). For example: > + > + struct kvm_device_attr st_base = { > + .group = KVM_DEV_ARM_PV_TIME_PADDR, > + .attr = KVM_DEV_ARM_PV_TIME_ST, > + .addr = (u64)(unsigned long)&st_paddr > + }; > + > + ioctl(pvtime_fd, KVM_SET_DEVICE_ATTR, &st_base); So the allocation itself is performed by the kernel? What are the ordering requirements between creating vcpus and the device? What are the alignment requirements for the base address? > + > +For migration (or save/restore) of a guest it is necessary to save the contents > +of the shared page(s) and later restore them. KVM_DEV_ARM_PV_TIME_STATE_SIZE > +provides the size of this data and KVM_DEV_ARM_PV_TIME_STATE allows the state > +to be read/written. Is the size variable depending on the number of vcpus? > + > +It is also necessary for the physical address to be set identically when > +restoring. > + > + void *save_state(int fd, u64 attr, u32 *size) { > + struct kvm_device_attr get_size = { > + .group = KVM_DEV_ARM_PV_TIME_STATE_SIZE, > + .attr = attr, > + .addr = (u64)(unsigned long)size > + }; > + > + ioctl(fd, KVM_GET_DEVICE_ATTR, get_size); > + > + void *buffer = malloc(*size); > + > + struct kvm_device_attr get_state = { > + .group = KVM_DEV_ARM_PV_TIME_STATE, > + .attr = attr, > + .addr = (u64)(unsigned long)size > + }; > + > + ioctl(fd, KVM_GET_DEVICE_ATTR, buffer); > + } > + > + void *st_state = save_state(pvtime_fd, KVM_DEV_ARM_PV_TIME_ST, &st_size); > + Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71AF1C31E40 for ; 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Sat, 03 Aug 2019 13:13:46 +0200 Date: Sat, 3 Aug 2019 12:13:43 +0100 From: Marc Zyngier To: Steven Price Subject: Re: [PATCH 1/9] KVM: arm64: Document PV-time interface Message-ID: <20190803121343.2f482200@why> In-Reply-To: <20190802145017.42543-2-steven.price@arm.com> References: <20190802145017.42543-1-steven.price@arm.com> <20190802145017.42543-2-steven.price@arm.com> Organization: Approximate X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: steven.price@arm.com, catalin.marinas@arm.com, pbonzini@redhat.com, rkrcmar@redhat.com, linux@armlinux.org.uk, will@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, peter.maydell@linaro.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on cheepnis.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190803_041359_392515_DEA8E51D X-CRM114-Status: GOOD ( 28.94 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: peter.maydell@linaro.org, kvm@vger.kernel.org, Radim =?UTF-8?B?S3LEjW3DocWZ?= , Catalin Marinas , Suzuki K Pouloze , linux-doc@vger.kernel.org, Russell King , linux-kernel@vger.kernel.org, James Morse , linux-arm-kernel@lists.infradead.org, Paolo Bonzini , Will Deacon , kvmarm@lists.cs.columbia.edu, Julien Thierry Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 2 Aug 2019 15:50:09 +0100 Steven Price wrote: [+Peter for the userspace aspect of things] Hi Steve, > Introduce a paravirtualization interface for KVM/arm64 based on the > "Arm Paravirtualized Time for Arm-Base Systems" specification DEN 0057A. > > This only adds the details about "Stolen Time" as the details of "Live > Physical Time" have not been fully agreed. > > User space can specify a reserved area of memory for the guest and > inform KVM to populate the memory with information on time that the host > kernel has stolen from the guest. > > A hypercall interface is provided for the guest to interrogate the > hypervisor's support for this interface and the location of the shared > memory structures. > > Signed-off-by: Steven Price > --- > Documentation/virtual/kvm/arm/pvtime.txt | 107 +++++++++++++++++++++++ > 1 file changed, 107 insertions(+) > create mode 100644 Documentation/virtual/kvm/arm/pvtime.txt > > diff --git a/Documentation/virtual/kvm/arm/pvtime.txt b/Documentation/virtual/kvm/arm/pvtime.txt > new file mode 100644 > index 000000000000..e6ae9799e1d5 > --- /dev/null > +++ b/Documentation/virtual/kvm/arm/pvtime.txt > @@ -0,0 +1,107 @@ > +Paravirtualized time support for arm64 > +====================================== > + > +Arm specification DEN0057/A defined a standard for paravirtualised time > +support for Aarch64 guests: nit: AArch64 > + > +https://developer.arm.com/docs/den0057/a Between this file and the above document, which one is authoritative? > + > +KVM/Arm64 implements the stolen time part of this specification by providing nit: KVM/arm64 > +some hypervisor service calls to support a paravirtualized guest obtaining a > +view of the amount of time stolen from its execution. > + > +Two new SMCCC compatible hypercalls are defined: > + > +PV_FEATURES 0xC5000020 > +PV_TIME_ST 0xC5000022 > + > +These are only available in the SMC64/HVC64 calling convention as > +paravirtualized time is not available to 32 bit Arm guests. > + > +PV_FEATURES > + Function ID: (uint32) : 0xC5000020 > + PV_func_id: (uint32) : Either PV_TIME_LPT or PV_TIME_ST > + Return value: (int32) : NOT_SUPPORTED (-1) or SUCCESS (0) if the relevant > + PV-time feature is supported by the hypervisor. How is PV_FEATURES discovered? Is the intention to make it a generic ARM-wide PV discovery mechanism, not specific to PV time? > + > +PV_TIME_ST > + Function ID: (uint32) : 0xC5000022 > + Return value: (int64) : IPA of the stolen time data structure for this > + (V)CPU. On failure: > + NOT_SUPPORTED (-1) > + Is the size implicit? What are the memory attributes? This either needs documenting here, or point to the right bit to the spec. > +Stolen Time > +----------- > + > +The structure pointed to by the PV_TIME_ST hypercall is as follows: > + > + Field | Byte Length | Byte Offset | Description > + ----------- | ----------- | ----------- | -------------------------- > + Revision | 4 | 0 | Must be 0 for version 0.1 > + Attributes | 4 | 4 | Must be 0 > + Stolen time | 8 | 8 | Stolen time in unsigned > + | | | nanoseconds indicating how > + | | | much time this VCPU thread > + | | | was involuntarily not > + | | | running on a physical CPU. > + > +The structure will be updated by the hypervisor periodically as time is stolen Is it really periodic? If so, when is the update frequency? > +from the VCPU. It will be present within a reserved region of the normal > +memory given to the guest. The guest should not attempt to write into this > +memory. There is a structure by VCPU of the guest. What if the vcpu writes to it? Does it get a fault? If there is a structure per vcpu, what is the layout in memory? How does a vcpu find its own data structure? Is that the address returned by PV_TIME_ST? > + > +User space interface > +==================== > + > +User space can request that KVM provide the paravirtualized time interface to > +a guest by creating a KVM_DEV_TYPE_ARM_PV_TIME device, for example: > + > + struct kvm_create_device pvtime_device = { > + .type = KVM_DEV_TYPE_ARM_PV_TIME, > + .attr = 0, > + .flags = 0, > + }; > + > + pvtime_fd = ioctl(vm_fd, KVM_CREATE_DEVICE, &pvtime_device); > + > +The guest IPA of the structures must be given to KVM. This is the base address nit: s/guest // > +of an array of stolen time structures (one for each VCPU). For example: > + > + struct kvm_device_attr st_base = { > + .group = KVM_DEV_ARM_PV_TIME_PADDR, > + .attr = KVM_DEV_ARM_PV_TIME_ST, > + .addr = (u64)(unsigned long)&st_paddr > + }; > + > + ioctl(pvtime_fd, KVM_SET_DEVICE_ATTR, &st_base); So the allocation itself is performed by the kernel? What are the ordering requirements between creating vcpus and the device? What are the alignment requirements for the base address? > + > +For migration (or save/restore) of a guest it is necessary to save the contents > +of the shared page(s) and later restore them. KVM_DEV_ARM_PV_TIME_STATE_SIZE > +provides the size of this data and KVM_DEV_ARM_PV_TIME_STATE allows the state > +to be read/written. Is the size variable depending on the number of vcpus? > + > +It is also necessary for the physical address to be set identically when > +restoring. > + > + void *save_state(int fd, u64 attr, u32 *size) { > + struct kvm_device_attr get_size = { > + .group = KVM_DEV_ARM_PV_TIME_STATE_SIZE, > + .attr = attr, > + .addr = (u64)(unsigned long)size > + }; > + > + ioctl(fd, KVM_GET_DEVICE_ATTR, get_size); > + > + void *buffer = malloc(*size); > + > + struct kvm_device_attr get_state = { > + .group = KVM_DEV_ARM_PV_TIME_STATE, > + .attr = attr, > + .addr = (u64)(unsigned long)size > + }; > + > + ioctl(fd, KVM_GET_DEVICE_ATTR, buffer); > + } > + > + void *st_state = save_state(pvtime_fd, KVM_DEV_ARM_PV_TIME_ST, &st_size); > + Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel