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Re: [PATCH v5 15/22] target/arm: Clean address for DC ZVA

From: Peter Maydell
Subject: Re: [PATCH v5 15/22] target/arm: Clean address for DC ZVA
Date: Tue, 18 Feb 2020 11:10:01 +0000

On Tue, 18 Feb 2020 at 00:50, Richard Henderson
<address@hidden> wrote:
> It isn't clear to me that DC ZVA does check tags.  There's no pseudocode for
> DC_ZVA, which is less helpful than it might be.
> I suppose one could infer it from "behaves as a set of stores to each byte
> within the block", but considering that stores are both checking or
> non-checking depending on addressing mode etc, I'd have preferred an explicit 
> note.
> So far I'm treating DC_ZVA as unchecked.

I think the spec is reasonably clear here. In D6.8 it says
"Unless an access is explicitly defined as a Tag Unchecked
access it is a Tag Checked access."
and then in D6.8.1:
"A cache maintenance by virtual address operation other than
DC ZVA generates a Tag Unchecked access."

So DC ZVA is Tag Checked, other DC ops that take a VA
are Tag Unchecked.

-- PMM

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