Re: [PATCH v19 20/20] KVM: arm64: CCA: Control user register access for Realms

[Gavin Shan <gshan@redhat.com>]

On 9/21/26 7:28 AM, Suzuki K Poulose wrote:
> From: Jean-Philippe Brucker <jean-philippe@linaro.org>
> 
> The RMM restricts the access to the register states that the host can
> read/modify for a given Realm.
> 
> e.g., At VCPU creation, can modify GPRS (x0-x30) and PC.
>        While servicing SMCCC calls via RSI_HOST_CALL or servicing PSCI
>        requests.
>        MMIO emulation in the unprotected space.
> 
> Additionally we use the sysreg configuration to advertise/configure the
> following Realm parameters, which are required before the Realm Descriptor
> :w
> is created:
>   - SVE Vector Length
>   - Number of HW Breakpoints/Watchpoints
>   - PMU Counters.
> 
> Thus KVM also additionally allows access to ID_AA64DFR0_EL1 and SVE_VLS for
> the configuration of Realm creation parameters. We don't support PMUs for
> the Realm VMs yet, so PMCR is not exposed.
> 
> The RMM makes similar restrictions for reading of the guest's registers
> (this is *confidential* compute after all), however we don't impose the
> restriction here. This allows the VMM to read (stale) values from the
> registers which might be useful to read back the initial values even if
> the RMM doesn't provide the latest version. For migration of a realm VM,
> a new interface will be needed so that the VMM can receive an
> (encrypted) blob of the VM's state.
> 
> Reflect the above in KVM_GET_REG_LIST, KVM_SET_ONE_REG calls.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> Co-developed-by: Steven Price <steven.price@arm.com>
> Signed-off-by: Steven Price <steven.price@arm.com>
> Co-developed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
> Changes since v18:
>   - Don't expose PMCR_EL0 to the userspace now, we could do that when we
>     support PMU
>   - Fix check patch warnings
> Changes since v17:
>    - Merge related changes into one single patch for the user set/get registers
>      I have retained the Review tags, as the code hasn't changed, just the patches
>      were merged into a single one with the same tags.
>    - Limit KVM_GET_REG_LIST to the allowed CORE registers.
> ---
>   arch/arm64/kvm/guest.c      | 63 +++++++++++++++++++++++++++++++++++++
>   arch/arm64/kvm/hypercalls.c |  4 +--
>   arch/arm64/kvm/sys_regs.c   | 28 +++++++++++++----
>   3 files changed, 87 insertions(+), 8 deletions(-)
> 

Reviewed-by: Gavin Shan <gshan@redhat.com>