On 2017/9/7 23:23, Marc Zyngier wrote: > On 07/09/17 16:03, gengdongjiu wrote: >>> On 07/09/17 12:49, gengdongjiu wrote: >>>> [...]
> > I really cannot think of a good reason why we'd want to do that. Playing > with set_fs() is almost universally wrong, and I'm certainly going to > oppose to any change in that area unless the code that calls set_fs() > has been made public and properly reviewed. Until then, UAO/PAN will > stay as they are unless you prove that our current code is wrong. Marc, sorry I have another question for the PAN. In the non-VHE mode, The host kernel is running in the EL1. Before host kernel enter guest, host OS will call 'HVC' instruction to do the world-switch, and the pstate.PAN will be saved into the SPSR_EL2. When world-switch back to host kernel from EL2, it will call 'eret' instruction to EL1 host, this 'eret' instruction will restore the SPSR_EL2 to the PSTATE. so the PSTATE.PAN will be restored. For the Non-VHE mode, in the EL2 where mainly have word-switch code, do you think it needs to reset the PSTATE.PAN? From the spec, it does not provide SCTLR_EL2.SPAN bit for non-VHE mode, so reset the PSTATE.PAN does not sure whether it is needed or whether affects the performance. If you think it is needed for El2 in Non-VHE mode, moving the reset PSTATE.PAN to the exception entry to EL2 may be better, such as "el1_sync", because host can also call 'hvc' instruction without guest running. > > M. >
