Re: [Xen-devel] [PATCH v4 09/15] xen: arm: Handle CP15 register traps from userspace

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Ian,

On 27/03/15 14:33, 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).
> 
> PMINTENSET, PMINTENCLR are EL1 only, but it is not clear whether
> attempts to access from EL0 will trap to EL1 or EL2, be conservative
> and handle EL0 access with an undef injection.
> 
> ACTLR is EL1 only and the ARM ARM states that HCR_EL2.TACR causes
> accesses from EL1 to trap. However remain conservative even here and
> handle accesses from EL0 by injecting an undef injection.
> 
> PMUSERENR is R/O at EL0 and we implement as RAZ/WI at EL1 as before.
> 
> The remaining PM* registers are accessible to EL0 only if
> PMUSERENR_EL0.EN is set, since we emulate this as RAZ/WI the bit is
> never set so we inject a trap on attempted access. We weren't
> previously handling PMCCNTR.
> 
> HSR_EC_CP15_32 should never be seen from a 64-bit guest, so BUG_ON if
> that occurs.
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Reviewed-by: Julien Grall <julien.grall@xxxxxxxxxx>

Regards,

-- 
Julien Grall

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