KVM: arm64: add workaround for Cortex-A57 erratum #852523

When restoring the system register state for an AArch32 guest at EL2,
writes to DACR32_EL2 may not be correctly synchronised by Cortex-A57,
which can lead to the guest effectively running with junk in the DACR
and running into unexpected domain faults.

This patch works around the issue by re-ordering our restoration of the
AArch32 register aliases so that they happen before the AArch64 system
registers. Ensuring that the registers are restored in this order
guarantees that they will be correctly synchronised by the core.

Cc: <stable@vger.kernel.org>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
index 8188f6ae8fc40fbd0e7518c99a97c59b73e91220..39aa322765f9fd8db6ab411131f2fce51d7e9429 100644 (file)
--- a/arch/arm64/kvm/hyp.S
+++ b/arch/arm64/kvm/hyp.S
@@ -745,6 +745,9 @@ ENTRY(__kvm_vcpu_run)
        // Guest context
        add     x2, x0, #VCPU_CONTEXT
 
+       // We must restore the 32-bit state before the sysregs, thanks
+       // to Cortex-A57 erratum #852523.
+       restore_guest_32bit_state
        bl __restore_sysregs
 
        skip_debug_state x3, 1f
@@ -752,7 +755,6 @@ ENTRY(__kvm_vcpu_run)
        kern_hyp_va x3
        bl      __restore_debug
 1:
-       restore_guest_32bit_state
        restore_guest_regs
 
        // That's it, no more messing around.