Hi Julien,
On Mon, Feb 05, 2018 at 06:04:25PM +0000, Julien Grall wrote:
> On 12/01/18 12:07, Christoffer Dall wrote:
> >VHE actually doesn't rely on clearing the VTTBR when returning to the
> >host kernel, and that is the current key mechanism of hyp_panic to
> >figure out how to attempt to return to a state good enough to print a
> >panic statement.
> >
> >Therefore, we split the hyp_panic function into two functions, a VHE and
> >a non-VHE, keeping the non-VHE version intact, but changing the VHE
> >behavior.
> >
> >The vttbr_el2 check on VHE doesn't really make that much sense, because
> >the only situation where we can get here on VHE is when the hypervisor
> >assembly code actually called into hyp_panic, which only happens when
> >VBAR_EL2 has been set to the KVM exception vectors. On VHE, we can
> >always safely disable the traps and restore the host registers at this
> >point, so we simply do that unconditionally and call into the panic
> >function directly.
> >
> >Acked-by: Marc Zyngier <marc.zyng...@arm.com>
> >Signed-off-by: Christoffer Dall <christoffer.d...@linaro.org>
> >---
> > arch/arm64/kvm/hyp/switch.c | 42 +++++++++++++++++++++++-------------------
> > 1 file changed, 23 insertions(+), 19 deletions(-)
> >
> >diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> >index 6fcb37e220b5..71700ecee308 100644
> >--- a/arch/arm64/kvm/hyp/switch.c
> >+++ b/arch/arm64/kvm/hyp/switch.c
> >@@ -419,10 +419,20 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
> > static const char __hyp_panic_string[] = "HYP panic:\nPS:%08llx PC:%016llx
> > ESR:%08llx\nFAR:%016llx HPFAR:%016llx PAR:%016llx\nVCPU:%p\n";
> > static void __hyp_text __hyp_call_panic_nvhe(u64 spsr, u64 elr, u64 par,
> >- struct kvm_vcpu *vcpu)
> >+ struct kvm_cpu_context
> >*__host_ctxt)
> > {
> >+ struct kvm_vcpu *vcpu;
> > unsigned long str_va;
> >+ vcpu = __host_ctxt->__hyp_running_vcpu;
> >+
> >+ if (read_sysreg(vttbr_el2)) {
> >+ __timer_disable_traps(vcpu);
> >+ __deactivate_traps(vcpu);
> >+ __deactivate_vm(vcpu);
> >+ __sysreg_restore_host_state(__host_ctxt);
> >+ }
> >+
> > /*
> > * Force the panic string to be loaded from the literal pool,
> > * making sure it is a kernel address and not a PC-relative
> >@@ -436,37 +446,31 @@ static void __hyp_text __hyp_call_panic_nvhe(u64 spsr,
> >u64 elr, u64 par,
> > read_sysreg(hpfar_el2), par, vcpu);
> > }
> >-static void __hyp_text __hyp_call_panic_vhe(u64 spsr, u64 elr, u64 par,
> >- struct kvm_vcpu *vcpu)
> >+static void __hyp_call_panic_vhe(u64 spsr, u64 elr, u64 par,
> >+ struct kvm_cpu_context *host_ctxt)
> > {
> >+ struct kvm_vcpu *vcpu;
> >+ vcpu = host_ctxt->__hyp_running_vcpu;
> >+
> >+ __deactivate_traps(vcpu);
> >+ __sysreg_restore_host_state(host_ctxt);
>
> I was about to ask why you keep this function around as it does nothing in
> VHE case. But I see that this will actually restore some values in a later
> patch.
>
> >+
> > panic(__hyp_panic_string,
> > spsr, elr,
> > read_sysreg_el2(esr), read_sysreg_el2(far),
> > read_sysreg(hpfar_el2), par, vcpu);
> > }
> >-static hyp_alternate_select(__hyp_call_panic,
> >- __hyp_call_panic_nvhe, __hyp_call_panic_vhe,
> >- ARM64_HAS_VIRT_HOST_EXTN);
>
> Out of interest, any specific rather to remove hyp_alternate_select and
> "open-code" it?
>
Not sure I understand your question.
Are you asking why I replace the hyp alternatives with the has_vhe()?
If so, has_vhe() uses a static key and should therefore have the same
performance characteristics, but I find the has_vhe() version below much
more readable.
> >-
> > void __hyp_text __noreturn hyp_panic(struct kvm_cpu_context *host_ctxt)
> > {
> >- struct kvm_vcpu *vcpu = NULL;
> >-
> > u64 spsr = read_sysreg_el2(spsr);
> > u64 elr = read_sysreg_el2(elr);
> > u64 par = read_sysreg(par_el1);
> >- if (read_sysreg(vttbr_el2)) {
> >- vcpu = host_ctxt->__hyp_running_vcpu;
> >- __timer_disable_traps(vcpu);
> >- __deactivate_traps(vcpu);
> >- __deactivate_vm(vcpu);
> >- __sysreg_restore_host_state(host_ctxt);
> >- }
> >-
> >- /* Call panic for real */
> >- __hyp_call_panic()(spsr, elr, par, vcpu);
> >+ if (!has_vhe())
> >+ __hyp_call_panic_nvhe(spsr, elr, par, host_ctxt);
> >+ else
> >+ __hyp_call_panic_vhe(spsr, elr, par, host_ctxt);
> > unreachable();
> > }
> >
>
Thanks,
-Christoffer
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