[PATCH] arm64: clear_page() shouldn't use DC ZVA when DCZID_EL0.DZP == 1

[Reiji Watanabe]

On Tue, Oct 26, 2021 at 2:06 AM Catalin Marinas <catalin.marinas at arm.com> wrote:
>
> On Mon, Oct 25, 2021 at 08:48:44PM -0700, Reiji Watanabe wrote:
> > Currently, clear_page() uses DC ZVA instruction unconditionally.  But it
> > should make sure that DCZID_EL0.DZP, which indicates whether or not use
> > of DC ZVA instruction is prohibited, is zero when using the instruction.
> > Use stp as memset does instead when DCZID_EL0.DZP == 1.
>
> For correctness, this is fine, but have you come across a system that
> has DZP == 1 (or hypervisor setting HCR_EL2.TDZ)?

We are thinking of setting HCR_EL2.TDZ considering live migration
support between two systems with different DCZID_EL0.BS.

Thanks,
Reiji