On Tue, 25 Nov 2025 at 16:09, Cornelia Huck <[email protected]> wrote: > > On Mon, Nov 24 2025, Peter Maydell <[email protected]> wrote: > > > On Wed, 19 Nov 2025 at 13:44, Cornelia Huck <[email protected]> wrote: > >> > >> This requires a bit of care, since we still have to handle the EL > >> specific part (DCZID_EL0.DZP). Callers can set/access dcz_blocksize > >> via a wrapper working on DCZID_EL.BS. > >> > >> KVM currently does not support DCZID_EL0 via ONE_REG, and actually > >> does not need to work with it, so provide a dummy value for now. > > > > That seems like an odd (unintended?) omission -- is it worth > > adding? (We would need to handle older kernels that don't > > expose it anyway, of course.) > > I'm not sure whether there's actually a usecase for KVM exposing this to > the VMM - AFAICS, KVM doesn't do anything special for DC ZVA and > friends, and doesn't tweak HCR_EL2.TDZ which would change behaviour.
I guess the only one I can think of is to correctly fail migration from a source CPU with a DCZID_EL0.BS that doesn't match the one on the destination CPU. (We can't lie to the guest about the blocksize as part of "tell the guest it has a different CPU type from the actual host" unless we want to trap and emulate all the DC ZVA etc insns...) thanks -- PMM
