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

commit 43297dda0a51e4ffed0888ce727c218cfb7474b6 upstream.

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.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
index 17a8fb14f428d47226edbeeb661e840ff53b8988..7bd37d05b4e8d0a58ef57bf1a02270368e9d2571 100644 (file)
--- a/arch/arm64/kvm/hyp.S
+++ b/arch/arm64/kvm/hyp.S
@@ -943,13 +943,15 @@ 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
        bl __restore_fpsimd
 
        skip_debug_state x3, 1f
        bl      __restore_debug
 1:
-       restore_guest_32bit_state
        restore_guest_regs
 
        // That's it, no more messing around.