kvm: arm/arm64: vgic-v3: Tighten synchronization for guests using v2 on v3

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Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=27e91ad1e746e341ca2312f29bccb9736be7b476
Commit:     27e91ad1e746e341ca2312f29bccb9736be7b476
Parent:     16ca6a607d84bef0129698d8d808f501afd08d43
Author:     Marc Zyngier <marc.zyngier at arm.com>
AuthorDate: Tue Mar 6 21:44:37 2018 +0000
Committer:  Marc Zyngier <marc.zyngier at arm.com>
CommitDate: Wed Mar 14 18:31:26 2018 +0000

    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.
    
    Cc: stable at vger.kernel.org
    Fixes: f68d2b1b73cc ("arm64: KVM: Implement vgic-v3 save/restore")
    Acked-by: Christoffer Dall <cdall at kernel.org>
    Reviewed-by: Andre Przywara <andre.przywara at arm.com>
    Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
---
 virt/kvm/arm/hyp/vgic-v3-sr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/arm/hyp/vgic-v3-sr.c b/virt/kvm/arm/hyp/vgic-v3-sr.c
index f5c3d6d7019e..b89ce5432214 100644
--- a/virt/kvm/arm/hyp/vgic-v3-sr.c
+++ b/virt/kvm/arm/hyp/vgic-v3-sr.c
@@ -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);
 	}