On Tue, Apr 12, 2022 at 11:40 PM Gavin Shan <gshan@xxxxxxxxxx> wrote: > > Hi Raghavendra, > > On 4/7/22 9:16 AM, Raghavendra Rao Ananta wrote: > > Add the documentation for the bitmap firmware registers in > > hypercalls.rst and api.rst. This includes the details for > > KVM_REG_ARM_STD_BMAP, KVM_REG_ARM_STD_HYP_BMAP, and > > KVM_REG_ARM_VENDOR_HYP_BMAP registers. > > > > Since the document is growing to carry other hypercall related > > information, make necessary adjustments to present the document > > in a generic sense, rather than being PSCI focused. > > > > Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxx> > > --- > > Documentation/virt/kvm/api.rst | 17 ++++ > > Documentation/virt/kvm/arm/hypercalls.rst | 95 ++++++++++++++++++----- > > 2 files changed, 94 insertions(+), 18 deletions(-) > > > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > > index d13fa6600467..e0107b157965 100644 > > --- a/Documentation/virt/kvm/api.rst > > +++ b/Documentation/virt/kvm/api.rst > > @@ -2542,6 +2542,23 @@ arm64 firmware pseudo-registers have the following bit pattern:: > > > > 0x6030 0000 0014 <regno:16> > > > > +arm64 bitmap feature firmware pseudo-registers have the following bit pattern:: > > + > > + 0x6030 0000 0016 <regno:16> > > + > > +The bitmap feature firmware registers exposes the hypercall services that are > > +available for userspace to configure. The set bits corresponds to the services > > +that are available for the guests to access. By default, KVM sets all the > > +supported bits during VM initialization. The userspace can discover the > > +available services via KVM_GET_ONE_REG, and write-back the bitmap corresponding > > +to the features that it wishes guests to see via KVM_SET_ONE_REG. > > + > > +Note: These registers are immutable once any of the vCPUs of the VM has run at > > +least once. A KVM_SET_ONE_REG in such a scenario will return a -EBUSY to userspace. > > +If there's no change in the value that's being written, 0 (success) is returned. > > + > > +(See Documentation/virt/kvm/arm/hypercalls.rst for more details.) > > + > > arm64 SVE registers have the following bit patterns:: > > > > 0x6080 0000 0015 00 <n:5> <slice:5> Zn bits[2048*slice + 2047 : 2048*slice] > > diff --git a/Documentation/virt/kvm/arm/hypercalls.rst b/Documentation/virt/kvm/arm/hypercalls.rst > > index d52c2e83b5b8..ccda9fc2d253 100644 > > --- a/Documentation/virt/kvm/arm/hypercalls.rst > > +++ b/Documentation/virt/kvm/arm/hypercalls.rst > > @@ -1,32 +1,32 @@ > > .. SPDX-License-Identifier: GPL-2.0 > > > > -========================================= > > -Power State Coordination Interface (PSCI) > > -========================================= > > +======================= > > +ARM Hypercall Interface > > +======================= > > > > -KVM implements the PSCI (Power State Coordination Interface) > > -specification in order to provide services such as CPU on/off, reset > > -and power-off to the guest. > > +KVM handles the hypercall services as requested by the guests. New hypercall > > +services are regularly made available by the ARM specification or by KVM (as > > +vendor services) if they make sense from a virtualization point of view. > > > > -The PSCI specification is regularly updated to provide new features, > > -and KVM implements these updates if they make sense from a virtualization > > -point of view. > > - > > -This means that a guest booted on two different versions of KVM can > > -observe two different "firmware" revisions. This could cause issues if > > -a given guest is tied to a particular PSCI revision (unlikely), or if > > -a migration causes a different PSCI version to be exposed out of the > > -blue to an unsuspecting guest. > > +This means that a guest booted on two different versions of KVM can observe > > +two different "firmware" revisions. This could cause issues if a given guest > > +is tied to a particular version of a hypercall service, or if a migration > > +causes a different version to be exposed out of the blue to an unsuspecting > > +guest. > > > > In order to remedy this situation, KVM exposes a set of "firmware > > pseudo-registers" that can be manipulated using the GET/SET_ONE_REG > > interface. These registers can be saved/restored by userspace, and set > > -to a convenient value if required. > > +to a convenient value as required. > > > > -The following register is defined: > > +The following registers are defined: > > > > * KVM_REG_ARM_PSCI_VERSION: > > > > + KVM implements the PSCI (Power State Coordination Interface) > > + specification in order to provide services such as CPU on/off, reset > > + and power-off to the guest. > > + > > - Only valid if the vcpu has the KVM_ARM_VCPU_PSCI_0_2 feature set > > (and thus has already been initialized) > > - Returns the current PSCI version on GET_ONE_REG (defaulting to the > > @@ -74,4 +74,63 @@ The following register is defined: > > KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED: > > The workaround is always active on this vCPU or it is not needed. > > > > -.. [1] https://developer.arm.com/-/media/developer/pdf/ARM_DEN_0070A_Firmware_interfaces_for_mitigating_CVE-2017-5715.pdf > > + > > +Bitmap Feature Firmware Registers > > +--------------------------------- > > + > > +Contrary to the above registers, the following registers exposes the hypercall > > +services in the form of a feature-bitmap to the userspace. This bitmap is > > +translated to the services that are available to the guest. There is a register > > +defined per service call owner and can be accessed via GET/SET_ONE_REG interface. > > + > > +By default, these registers are set with the upper limit of the features that > > +are supported. This way userspace can discover all the electable hypercall services > > +via GET_ONE_REG. The user-space can write-back the desired bitmap back via > > +SET_ONE_REG. The features for the registers that are untouched, probably because > > +userspace isn't aware of them, will be exposed as is to the guest. > > + > > +Note that KVM would't allow the userspace to configure the registers anymore once > > +any of the vCPUs has run at least once. Instead, it will return a -EBUSY. However, > > +if there's no change in the incoming value, it simply returns a success. > > + > > It would be better to replace "a success" with "zero", to be consistent > with "-EBUSY". The suggestion may be invalid if the code needs changes > based on Marc's suggestions. > Yes, I agree. Mentioning 'zero' makes more sense. However, I would be scraping off this logic and return -EBUSY for all the writes after the VM has started. > > +The psuedo-firmware bitmap register are as follows: > > + > > +* KVM_REG_ARM_STD_BMAP: > > + Controls the bitmap of the ARM Standard Secure Service Calls. > > + > > + The following bits are accepted: > > + > > + Bit-0: KVM_REG_ARM_STD_BIT_TRNG_V1_0: > > + The bit represents the services offered under v1.0 of ARM True Random > > + Number Generator (TRNG) specification, ARM DEN0098. > > + > > +* KVM_REG_ARM_STD_HYP_BMAP: > > + Controls the bitmap of the ARM Standard Hypervisor Service Calls. > > + > > + The following bits are accepted: > > + > > + Bit-0: KVM_REG_ARM_STD_HYP_BIT_PV_TIME: > > + The bit represents the Paravirtualized Time service as represented by > > + ARM DEN0057A. > > + > > +* KVM_REG_ARM_VENDOR_HYP_BMAP: > > + Controls the bitmap of the Vendor specific Hypervisor Service Calls. > > + > > + The following bits are accepted: > > + > > + Bit-0: KVM_REG_ARM_VENDOR_HYP_BIT_FUNC_FEAT > > + The bit represents the ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID > > + function-id > > + > > + Bit-1: KVM_REG_ARM_VENDOR_HYP_BIT_PTP: > > + The bit represents the Precision Time Protocol KVM service. > > + > > +Errors: > > + > > + ======= ============================================================= > > + -ENOENT Unknown register accessed. > > + -EBUSY Attempt a 'write' to the register after the VM has started. > > + -EINVAL Invalid bitmap written to the register. > > + ======= ============================================================= > > + > > +.. [1] https://developer.arm.com/-/media/developer/pdf/ARM_DEN_0070A_Firmware_interfaces_for_mitigating_CVE-2017-5715.pdf > > \ No newline at end of file > > > > Thanks, > Gavin > Regards, Raghavendra _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
