[PATCH v2 03/11] KVM: arm64: Change hyp_panic()s dependency on tpidr_el2

Hi Christoffer,

On 17/09/17 15:43, Christoffer Dall wrote:

On Tue, Aug 08, 2017 at 05:46:08PM +0100, James Morse wrote:

quoted

Make tpidr_el2 a cpu-offset for per-cpu variables in the same way the
host uses tpidr_el1. This lets tpidr_el{1,2} have the same value, and
on VHE they can be the same register.

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.

quoted

diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index 945e79c641c4..235d615cee30 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c

@@ -286,9 +286,9 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
 	u64 exit_code;
 
 	vcpu = kern_hyp_va(vcpu);
-	write_sysreg(vcpu, tpidr_el2);
 
 	host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
+	host_ctxt->__hyp_running_vcpu = vcpu;

I'm fine with this for now, but eventually when we optimize KVM further
we may want to avoid doing this in every world-switch.  One option is to
just set this pointer in vcpu_get and vcpu_load, but would it also be
possible to use the kvm_arm_running_vcpu per-cpu array directly?

Yes, that would have been better, I didn't know that existed...
After this point we can find per-cpu variables easily, they just need mapping to
HYP.

This pointer is just for the panic message, I'm not sure how useful it is.
For kdump the kvm_arm_running_vcpu array holds the same information, so is
printing this out just so we can spot if its totally-bogus?


As your fine with this for now, I'll put tidying it up on my todo list...

quoted

 	guest_ctxt = &vcpu->arch.ctxt;
 
 	__sysreg_save_host_state(host_ctxt);

Reviewed-by: Christoffer Dall <redacted>

Thanks!

James