Hello Christoffer, I agree with both of you points. What I found different in 2 approaches is that in your approach S->Monitor->NS->Hyp using svc and hvc While the other approach is setting the M bits directly in cpsr Xen uses the following cpsid aif, #0x16 /* Enter Monitor Mode*/ .... ... mrs r0, cpsr /* Copy the CPSR */ add r0, r0, #0x4 /* 0x16 (Monitor) -> 0x1a (Hyp) */ msr spsr_cxsf, r0 /* into the SPSR */ movs pc, r3 /* Exception-return into Hyp mode */ The second one is a bit simpler as it does not involve fault handlers. I was just suggesting that the best approach to be used ... Best Regards, mj On 9/20/13, Christoffer Dall <christoffer.dall@xxxxxxxxxx> wrote: > On Fri, Sep 20, 2013 at 01:27:48AM +0530, Mj Embd wrote: >> two quick points >> (a) xen already has a mode_switch code, so AFAIK xen might not use it >> (as suggested by comment in another patch in this patch set) > > For KVM the boot procedure for Hyp mode is quite clearly defined: the > kernel must be booted in Hyp mode. > > I was under the impression that Xen wanted to use the same paradigm and > rely on bootloaders to switch to Hyp mode and thereby get rid of the > code in Xen. > >> (b) There are 2 methods of switching from Secure to Hyp mode >> one you have proposed another implemented in xen. I was suggesting >> take the best approach >> > > Can you please be more specific? Not everyone here knows the Xen > low-level mode switch details by heart. As far as I know, there is only > one architecturally defined proper mode to switch from secure mode to > non-secure mode, and the state that needs to be configured for Hyp-mode > and NS-mode is well defined. Obviously two implementation can do things > differently (different order, different programminge environment, etc.) > but that doesn't mean one is better than the other. > > I think it would be more productive if you can simply look at this code > and if you think some things are done more efficiently in Xen, please > comment on that, which would be very helpful. I'm afraid there's no > magic way to apply a block of Xen code into U-Boot wihtout manual > adjustment anyway, or the other way around for that matter. > > -Christoffer > -- -mj _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
