[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 4/4] xen/public: arm: rework the macro set_xen_guest_handle_raw
On Wed, 2015-11-04 at 14:42 +0000, Julien Grall wrote: > On 04/11/15 14:29, Ian Campbell wrote: > > > > > > This looses out on the arm32 hypervisor sanity checking that > > > > > > the > > > > > > padding > > > > > > bytes are 0 (as required by the ABI) but TBH I haven't checked > > > > > > that > > > > > > the > > > > > > current version has that property either. > > > > > > > > > > It's done during the assignation by the compiler: > > > > > > > > > > (hnd).q = (uint64_t)(uintptr_t)(val); > > > > > > > > I meant on the reading side. > > > > > > It's the responsibility of the caller to zero the padding. There is > > > nothing to do on the reading side, the hypervisor will use "p" which > > > will be the size of the natural pointer. > > > > For a 32-bit Xen the check would be that a guest was not inadvertently > > violating this rule, such a guest would crash if it was run on a 64-bit > > hypervisor (which would see the non-zero padding as part of the > > pointer), > > by rejecting such cases on 32-bit Xen we avoid such guests becoming > > established and therefore presenting a case for us to relax this rule > > in > > one way or another. > > It would add overhead each time we want to copy to/from the guest memory. I was simply commenting that the approach taken here might be removing such a check _if_ it exists today, and as I said up front I'm not sure we have such a check right now or not. I'm not suggesting you add one as a new check, just that _if_ it already exists then it being removed needs to be considered. Ian. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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