Re: [Xen-devel] [PATCH 5/9] xen: arm: Handle CP15 register traps from userspace

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Ian,

On 09/09/14 09:23, Ian Campbell wrote:
> Previously userspace access to PM* would have been incorrectly (but benignly)
> implemented as RAZ/WI when running on a 32-bit kernel and would cause a
> hypervisor exception (host crash) when running a 64-bit kernel (this was
> already solved via the fix to XSA-102).
>
> CLIDR, CCSIDR, DCCISW, ACTLR, PMINTENSET, PMINTENCLR are EL1 only, attempts to
> access from EL0 will trap to EL1 not to us, hence BUG_ON is appropriate now.
In the unlikely case it happens, I don't think it will harm Xen, but 
only the guest. So is the BUG_ON really necessary on these registers?
I think we should use BUG_ON when we know that it will harm the Xen and 
it's not possible to come back from the state.
Regards,


--
Julien Grall

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