On Tue, 19 May 2026, Eric Auger wrote:
If the host supports KVM_CAP_ARM_SUPPORTED_REG_MASK_RANGES and
KVM_ARM_GET_REG_WRITABLE_MASKS ioctl successfully retrieved the mask
of writable fields for all ID regs, expose uint64 SYSREG properties
for all the writable ID reg fields exposed by the host kernel which
can be matched in target/arm/cpu-idregs.h.inc.
Properties are named SYSREG_<REG>_<FIELD> with REG and FIELD
being those used ARCHMRS Registers.json.
When such properties are set, they override the default field value
retrieved from the host and reinjected into KVM. Then the actual value
being applied at KVM depends on the register, ie. it can be sanitized.
In case the field value is rejected by KVM, the vpcu init fails.
Anyway there is a first attempt to write back this value into KVM.
Then legacy CPU options (virtualization, secure, ...) can still
override the previous value. So low level IDREG field properties
apply before the legacy ones.
An example of invocation is:
-cpu host,SYSREG_ID_AA64MMFR0_EL1_ECV=0x0
which sets ECV field of ID_AA64MMFR0_EL1 to 0 (enhanced counter
virtualization).
Signed-off-by: Eric Auger <[email protected]>
Signed-off-by: Cornelia Huck <[email protected]>
Reviewed-by: Sebastian Ott <[email protected]>
