KVM: arm64: VHE: Synchronize restore of host debug registers

When KVM runs in non-protected VHE mode, there's no context
synchronization event between __debug_switch_to_host() restoring the
host debug registers and __kvm_vcpu_run() unmasking debug exceptions.
Due to this, it's theoretically possible for the host to take an
unexpected debug exception due to the stale guest configuration.

This cannot happen in NVHE/HVHE mode as debug exceptions are masked in
the hyp code, and the exception return to the host will provide the
necessary context synchronization before debug exceptions can be taken.

For now, avoid the problem by adding an ISB after VHE hyp code restores
the host debug registers.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Will Deacon <will@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20250617133718.4014181-2-mark.rutland@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

diff --git a/arch/arm64/kvm/hyp/include/hyp/debug-sr.h b/arch/arm64/kvm/hyp/include/hyp/debug-sr.h
index 502a5b73ee70c21f59bf00d19ab8450d2b14943c..73881e1dc26794f7a979a1157b4386e70fba5e69 100644 (file)
--- a/arch/arm64/kvm/hyp/include/hyp/debug-sr.h
+++ b/arch/arm64/kvm/hyp/include/hyp/debug-sr.h
@@ -167,6 +167,9 @@ static inline void __debug_switch_to_host_common(struct kvm_vcpu *vcpu)
 
        __debug_save_state(guest_dbg, guest_ctxt);
        __debug_restore_state(host_dbg, host_ctxt);
+
+       if (has_vhe())
+               isb();
 }
 
 #endif /* __ARM64_KVM_HYP_DEBUG_SR_H__ */