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

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 10/09/14 02:48, Ian Campbell wrote:
> On Tue, 2014-09-09 at 16:42 -0700, Julien Grall wrote:
> > 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.
> AIUI it would be a hardware bug to see these traps in Xen. I think a
> BUG_ON is acceptable for such an occurrence.
I would turn into an ASSERT to avoid checking it in non-debug build.

Regards,

--
Julien Grall

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