Re: [Xen-devel] [PATCH v2 04/15] xen/arm: vgic-v3: Correctly handle RAZ/WI registers

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2015-02-02 at 15:59 +0000, Julien Grall wrote:
> Hi Ian,
> 
> On 02/02/15 15:24, Ian Campbell wrote:
> > On Thu, 2015-01-29 at 18:25 +0000, Julien Grall wrote:
> >> Some of the registers are accessible via multiple size (see 
> >> GICD_IPRIORITYR*).
> >>
> >> Thoses registers are misimplemented when they should be RAZ. Only
> > 
> > "Those" and "incorrectly implemented".
> > 
> >> word-access size are currently allowed for them.
> >>
> >> To avoid further issues, introduce different label following the 
> >> access-size
> >> of the registers:
> >>     - read_as_zero_64 and write_ignore_64: Used for registers accessible
> >>     via a double-word.
> >>     - read_as_zero_32 and write_ignore_32: Used for registers accessible
> >>     via a word.
> > 
> > 5.1.3 suggests there are at least some 64-bit registers where it ought
> > to be possible to read the upper and lower halves independently. Don't
> > you need to support that?
> 
> Only when the system is supporting AArch32. If the system only supports
> AArch64, 64-bit registers can only be read via a 64-bit access.
> 
> I don't think we actually support AArch32 on the vGICv3 drivers. And we
> don't emulate 32-bits access on 64-bit registers.

It's certainly our intention in general to support arm32 guest kernels
on arm64, the v3 vgic may not reach that aspiration though.

Ian.


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