Re: [PATCH 2/4] arm64: KVM: add missing dsb before invalidating Stage-2 TLBs

Will Deacon
2013-07-19T14:33:07Z

On Fri, Jul 19, 2013 at 02:53:53PM +0100, Marc Zyngier wrote:
> When performing a Stage-2 TLB invalidation, it is necessary to
> make sure the write to the page tables is observable by all CPUs.
>
> For this purpose, add a dsb instruction to __kvm_tlb_flush_vmid_ipa
> before doing the TLB invalidation itself.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> arch/arm64/kvm/hyp.S | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
> index 218802f..e1ccfcc 100644
> --- a/arch/arm64/kvm/hyp.S
> +++ b/arch/arm64/kvm/hyp.S
> @@ -604,6 +604,8 @@ END(__kvm_vcpu_run)
>
> // void __kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa);
> ENTRY(__kvm_tlb_flush_vmid_ipa)
> + dsb ishst // Make sure previous writes are observable
> +
> kern_hyp_va x0
> ldr x2, [x0, #KVM_VTTBR]
> msr vttbr_el2, x2
> --
> 1.8.2.3

I don't think the comment adds anything to this code. Also, why don't you
need similar barriers for the cases where you clobber the entire TLB (e.g.
__kvm_flush_vm_context)?

Will