On 07/09/17 12:49, gengdongjiu wrote: > > > On 2017/9/7 18:13, Marc Zyngier wrote: >> On 07/09/17 11:05, gengdongjiu wrote: >>> Hi James, >>> >>> On 2017/9/7 17:20, James Morse wrote: >>>> Hi Dongjiu Geng, >>>> >>>> On 07/09/17 06:54, Dongjiu Geng wrote: >>>>> In VHE mode, host kernel runs in the EL2 and can enable >>>>> 'User Access Override' when fs==KERNEL_DS so that it can >>>>> access kernel memory. However, PSTATE.UAO is set to 0 on >>>>> an exception taken from EL1 to EL2. Thus when VHE is used >>>>> and exception taken from a guest UAO will be disabled and >>>>> host will use the incorrect PSTATE.UAO. So check and reset >>>>> the PSTATE.UAO when switching to host. >>>> >>>> This would only be a problem if KVM were calling into world-switch with >>>> fs==KERNEL_DS. I can't see where this happens. >>> Not only KVM, may also kernel sets the fs == KERNEL_DS before calling into world-switch >> >> How? Please describe the exact sequence of event that lead to this >> situation with the current code base. > > Hi Marc, > > Different tasks have different fs, such as USER_DS or KERNEL_DS. In the context switch, it will restore the > task's fs. Thus, that depends on task itself, as shown below code. UAO is different with PAN, PAN will be always enabled if > hardware CPU supports PAN feature, but UAO is dynamical change. You haven't answered my question: There is exactly one point where we enter the world-switch. Show me that, at this point, PSTATE.UAO *before* the call is different from PSTATE.UAO after the call. Give me the exact sequence of event that leads to this situation. Show me a stack trace. Until you do this, I will ignore any further comment coming from you on this subject. Thanks, M. -- Jazz is not dead. It just smells funny...
