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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1i2X5N-0000Gl-Hi; Tue, 27 Aug 2019 08:44:17 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1i2X5H-0000Fg-KH for linux-arm-kernel@lists.infradead.org; Tue, 27 Aug 2019 08:44:13 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CF7B9337; Tue, 27 Aug 2019 01:44:08 -0700 (PDT) Received: from localhost (e113682-lin.copenhagen.arm.com [10.32.144.41]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6222B3F246; Tue, 27 Aug 2019 01:44:08 -0700 (PDT) Date: Tue, 27 Aug 2019 10:44:07 +0200 From: Christoffer Dall To: Steven Price Subject: Re: [PATCH v3 01/10] KVM: arm64: Document PV-time interface Message-ID: <20190827084407.GA6541@e113682-lin.lund.arm.com> References: <20190821153656.33429-1-steven.price@arm.com> <20190821153656.33429-2-steven.price@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190821153656.33429-2-steven.price@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190827_014411_753071_EA8C497A X-CRM114-Status: GOOD ( 27.98 ) 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: kvm@vger.kernel.org, linux-doc@vger.kernel.org, Marc Zyngier , linux-kernel@vger.kernel.org, Russell King , Catalin Marinas , Paolo Bonzini , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org 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 Wed, Aug 21, 2019 at 04:36:47PM +0100, 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/virt/kvm/arm/pvtime.txt | 100 ++++++++++++++++++++++++++ > 1 file changed, 100 insertions(+) > create mode 100644 Documentation/virt/kvm/arm/pvtime.txt > > diff --git a/Documentation/virt/kvm/arm/pvtime.txt b/Documentation/virt/kvm/arm/pvtime.txt > new file mode 100644 > index 000000000000..1ceb118694e7 > --- /dev/null > +++ b/Documentation/virt/kvm/arm/pvtime.txt > @@ -0,0 +1,100 @@ > +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. The existence of > +the PV_FEATURES hypercall should be probed using the SMCCC 1.1 ARCH_FEATURES > +mechanism before calling it. > + > +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) > + > +The IPA returned by PV_TIME_ST should be mapped by the guest as normal memory > +with inner and outer write back caching attributes, in the inner shareable > +domain. A total of 16 bytes from the IPA returned are guaranteed to be > +meaningfully filled by the hypervisor (see structure below). > + > +PV_TIME_ST returns the structure for the calling VCPU. > + > +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 prior to scheduling a 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 per 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: > + I feel it would be more consistent to have the details of this in Documentation/virt/kvm/devices/arm-pv-time.txt and refer to this document from here. > + 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); > + > +Creation of the device should be done after creating the vCPUs of the virtual > +machine. > + > +The 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). The base address > +must be page aligned. The size must be at least 64 * number of VCPUs and be a > +multiple of PAGE_SIZE. > + > +The memory for these structures should be added to the guest in the usual > +manner (e.g. using KVM_SET_USER_MEMORY_REGION). > + > +For example: > + > + struct kvm_dev_arm_st_region region = { > + .gpa = , > + .size = > + }; > + > + struct kvm_device_attr st_base = { > + .group = KVM_DEV_ARM_PV_TIME_PADDR, > + .attr = KVM_DEV_ARM_PV_TIME_ST, > + .addr = (u64)®ion > + }; > + > + ioctl(pvtime_fd, KVM_SET_DEVICE_ATTR, &st_base); > -- > 2.20.1 > Thanks, Christoffer _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel