Hi Christoffer, On 06/06/17 20:45, Christoffer Dall wrote: > On Mon, May 15, 2017 at 06:43:51PM +0100, James Morse wrote: >> KVM calls hyp_panic() when anything unexpected happens. This may occur >> while a guest owns the EL1 registers. KVM stashes the vcpu pointer in >> tpidr_el2, which it uses to find the host context in order to restore >> the host EL1 registers before parachuting into the host's panic(). >> >> The host context is a struct kvm_cpu_context allocated in the per-cpu >> area, and mapped to hyp. Given the per-cpu offset for this CPU, this is >> easy to find. Change hyp_panic() to take a pointer to the >> struct kvm_cpu_context. Wrap these calls with an asm function that >> retrieves the struct kvm_cpu_context from the host's per-cpu area. >> >> Copy the per-cpu offset from the hosts tpidr_el1 into tpidr_el2 during >> kvm init. (Later patches will make this unnecessary for VHE hosts) >> >> We print out the vcpu pointer as part of the panic message. Add a back >> reference to the 'running vcpu' in the host cpu context to preserve this. >> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S >> index fce7cc507e0a..0f83e7e402ad 100644 >> --- a/arch/arm64/kvm/hyp/hyp-entry.S >> +++ b/arch/arm64/kvm/hyp/hyp-entry.S >> @@ -163,6 +163,13 @@ ENTRY(__hyp_do_panic) >> eret >> ENDPROC(__hyp_do_panic) >> >> +ENTRY(__hyp_panic) >> + ldr x0, =kvm_host_cpu_state > > Why is this guaranteed to give us a valid EL2 address? ... it doesn't. Its a host address from the constant pool which is used by hyp-panic as __host_ctxt: > void __hyp_text __noreturn hyp_panic(struct kvm_cpu_context *__host_ctxt); and fixed up with: > host_ctxt = kern_hyp_va(__host_ctxt); to give us the EL2 address before we access it. For VHE the last step is a nop as the host address can be accessed directly. I will add a comment here explaining this. Thanks! James -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
