On Mon, 22 Jul 2019 at 12:19, Alex Bennée <alex.ben...@linaro.org> wrote: > > While most features are now detected by probing the ID_* registers > kernels can (and do) use MIDR_EL1 for working out of they have to > apply errata. This can trip up warnings in the kernel as it tries to > work out if it should apply workarounds to features that don't > actually exist in the reported CPU type. > > Avoid this problem by synthesising our own MIDR value using the > reserved value of 0 for the implementer and encoding the moving feast > that is the QEMU version string into the other fields.
Exposing the QEMU_VERSION_* information to the guest is usually not a good plan. For instance it means that the MIDR will mysteriously change if you save a VM on one version of QEMU and restore it on another. We went through a while back carefully removing places where we'd exposed the version number to the guest (have a look at the qemu_hw_version() stuff which has to jump through hoops so that old versioned machines like pc-1.5 report the old "1.5" version number, and any QEMU 2.5 and above now reports "2.5+"...) thanks -- PMM
