On 10/3/25 06:14, Julien Grall wrote: > Hi Demi, > > On 02/10/2025 19:27, Demi Marie Obenour wrote: >> On 10/2/25 06:10, Andrew Cooper wrote: >>> On 01/10/2025 9:01 pm, Milan Djokic wrote: >>>> Signed-off-by: Milan Djokic <[email protected]> >>>> >>>> --- >>>> XEN_DOMCTL_get_address_size hypercall is not implemented for arm (only for >>>> x86) >>>> It would be useful to have this hypercall supported for arm64, in order to >>>> get >>>> current guest addressing mode and also to verify that >>>> XEN_DOMCTL_set_address_size >>>> performs switch to target addressing mode (instead of relying on its >>>> returned error code only). >>> >>> Please don't copy this misfeature of x86 PV guests into ARM. >>> >>> Letting domains be of variable bitness after domain create leads to a >>> whole lot of bugs, many security relevant. >>> >>> 32bit vs 64bit should be an input to domain_create(), not something that >>> is edited after the domain has been constructed. >> >> Does this mean that Xen guests cannot support multiarch? > > I can't speak for x86. But for Arm, the endianess of EL1 (OS) is fixed > when the vCPU is booting. You could in theory have a domain with a mix > of 64-bit and 32-bit vCPUs. But that's not supported by Xen (all vCPUs > should have the same bitness) and also I am not aware of any mainstream > OS able to deal with multiple bitness. Most likely, you will need to run > two OSes and create your custom OS. > > Also, I believe XEN_DOMCTL_get_address_size would not be suitable for > such setup.
I meant multiarch in userspace. Running a 32-bit kernel makes no sense. If that is something Arm OSs just don't support that's fine too. -- Sincerely, Demi Marie Obenour (she/her/hers)
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