On Tue, 03 May 2022 00:38:50 +0100, Raghavendra Rao Ananta <rananta@xxxxxxxxxx> 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> > Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx> > --- > Documentation/virt/kvm/api.rst | 16 ++++ > Documentation/virt/kvm/arm/hypercalls.rst | 94 ++++++++++++++++++----- > 2 files changed, 92 insertions(+), 18 deletions(-) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index 4a900cdbc62e..8ae638be79fd 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -2542,6 +2542,22 @@ 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. > + The placement is odd, as SVE uses ID 0x0015, and is *after* this. > +(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..383ca766cf36 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 +74,62 @@ 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. > + Formatting is a bit off. We try to stay within the 80 cols format for text documents such as this. > +The psuedo-firmware bitmap register are as follows: Typo. > + > +* 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 > + and ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID function-ids. > + > + 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 > -- > 2.36.0.464.gb9c8b46e94-goog > > Thanks, M. -- Without deviation from the norm, progress is not possible.
