FAILED: patch "[PATCH] kvm: arm/arm64: vgic-v3: Tighten synchronization for guests" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Marc Zyngier <[email protected]>
Date: Tue, 6 Mar 2018 21:44:37 +0000
Subject: [PATCH] kvm: arm/arm64: vgic-v3: Tighten synchronization for guests
using v2 on v3

On guest exit, and when using GICv2 on GICv3, we use a dsb(st) to force synchronization between the memory-mapped guest view and the system-register view that the hypervisor uses.

This is incorrect, as the spec calls out the need for "a DSB whose required access type is both loads and stores with any Shareability attribute", while we're only synchronizing stores.

We also lack an isb after the dsb to ensure that the latter has actually been executed before we start reading stuff from the sysregs.

The fix is pretty easy: turn dsb(st) into dsb(sy), and slap an isb() just after.

index f5c3d6d7019e..b89ce5432214 100644
@@ -215,7 +215,8 @@ void __hyp_text __vgic_v3_save_state(struct kvm_vcpu *vcpu)
 	 * are now visible to the system register interface.
 	 */
 	if (!cpu_if->vgic_sre) {
-		dsb(st);
+		dsb(sy);
+		isb();
 		cpu_if->vgic_vmcr = read_gicreg(ICH_VMCR_EL2);
 	}