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Mon, 5 Aug 2019 11:26:25 +0800 (CST) Received: from [127.0.0.1] (10.184.12.158) by DGGEMS402-HUB.china.huawei.com (10.3.19.202) with Microsoft SMTP Server id 14.3.439.0; Mon, 5 Aug 2019 11:26:17 +0800 Subject: Re: [PATCH 1/9] KVM: arm64: Document PV-time interface To: Steven Price References: <20190802145017.42543-1-steven.price@arm.com> <20190802145017.42543-2-steven.price@arm.com> From: Zenghui Yu Message-ID: <3bdd764a-b6f5-d17e-a703-d8eb13838efc@huawei.com> Date: Mon, 5 Aug 2019 11:23:30 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:64.0) Gecko/20100101 Thunderbird/64.0 MIME-Version: 1.0 In-Reply-To: <20190802145017.42543-2-steven.price@arm.com> Content-Language: en-US X-Originating-IP: [10.184.12.158] X-CFilter-Loop: Reflected Cc: kvm@vger.kernel.org, linux-doc@vger.kernel.org, Catalin Marinas , Russell King , linux-kernel@vger.kernel.org, Marc Zyngier , Paolo Bonzini , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org 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-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu Hi Steven, On 2019/8/2 22:50, Steven Price wrote: > 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 ^^^^^^^ This directory has been renamed recently, see: https://patchwork.ozlabs.org/patch/1136104/ Zenghui > > 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: > + > +https://developer.arm.com/docs/den0057/a > + > +KVM/Arm64 implements the stolen time part of this specification by providing > +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. > + > +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) > + > +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 > +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. > + > +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 > +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); > + > +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. > + > +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); > + > _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm