3 files changed, 61 insertions, 3 deletions

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index b5926ee..12ee62d 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -124,7 +124,38 @@ ENTRY(__guest_exit)
 	// Now restore the host regs
 	restore_callee_saved_regs x2
 
-	ret
+	// If we have a pending asynchronous abort, now is the
+	// time to find out. From your VAXorcist book, page 666:
+	// "Threaten me not, oh Evil one!  For I speak with
+	// the power of DEC, and I command thee to show thyself!"
+	mrs	x2, elr_el2
+	mrs	x3, esr_el2
+	mrs	x4, spsr_el2
+	mov	x5, x0
+
+	dsb	sy		// Synchronize against in-flight ld/st
+	msr	daifclr, #4	// Unmask aborts
+
+	// This is our single instruction exception window. A pending
+	// SError is guaranteed to occur at the earliest when we unmask
+	// it, and at the latest just after the ISB.
+	.global	abort_guest_exit_start
+abort_guest_exit_start:
+
+	isb
+
+	.global	abort_guest_exit_end
+abort_guest_exit_end:
+
+	// If the exception took place, restore the EL1 exception
+	// context so that we can report some information.
+	// Merge the exception code with the SError pending bit.
+	tbz	x0, #ARM_EXIT_WITH_SERROR_BIT, 1f
+	msr	elr_el2, x2
+	msr	esr_el2, x3
+	msr	spsr_el2, x4
+	orr	x0, x0, x5
+1:	ret
 ENDPROC(__guest_exit)
 
 ENTRY(__fpsimd_guest_restore)
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index d2f6640..4e92399 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -126,6 +126,28 @@ el1_error:
 	mov	x0, #ARM_EXCEPTION_EL1_SERROR
 	b	__guest_exit
 
+el2_error:
+	/*
+	 * Only two possibilities:
+	 * 1) Either we come from the exit path, having just unmasked
+	 *    PSTATE.A: change the return code to an EL2 fault, and
+	 *    carry on, as we're already in a sane state to handle it.
+	 * 2) Or we come from anywhere else, and that's a bug: we panic.
+	 *
+	 * For (1), x0 contains the original return code and x1 doesn't
+	 * contain anything meaningful at that stage. We can reuse them
+	 * as temp registers.
+	 * For (2), who cares?
+	 */
+	mrs	x0, elr_el2
+	adr	x1, abort_guest_exit_start
+	cmp	x0, x1
+	adr	x1, abort_guest_exit_end
+	ccmp	x0, x1, #4, ne
+	b.ne	__hyp_panic
+	mov	x0, #(1 << ARM_EXIT_WITH_SERROR_BIT)
+	eret
+
 ENTRY(__hyp_do_panic)
 	mov	lr, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT |\
 		      PSR_MODE_EL1h)
@@ -150,7 +172,6 @@ ENDPROC(\label)
 	invalid_vector	el2h_sync_invalid
 	invalid_vector	el2h_irq_invalid
 	invalid_vector	el2h_fiq_invalid
-	invalid_vector	el2h_error_invalid
 	invalid_vector	el1_sync_invalid
 	invalid_vector	el1_irq_invalid
 	invalid_vector	el1_fiq_invalid
@@ -168,7 +189,7 @@ ENTRY(__kvm_hyp_vector)
 	ventry	el2h_sync_invalid		// Synchronous EL2h
 	ventry	el2h_irq_invalid		// IRQ EL2h
 	ventry	el2h_fiq_invalid		// FIQ EL2h
-	ventry	el2h_error_invalid		// Error EL2h
+	ventry	el2_error			// Error EL2h
 
 	ventry	el1_sync			// Synchronous 64-bit EL1
 	ventry	el1_irq				// IRQ 64-bit EL1
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index 8246de2..8b81cc6 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -292,6 +292,12 @@ again:
 	exit_code = __guest_enter(vcpu, host_ctxt);
 	/* And we're baaack! */
 
+	/*
+	 * We're using the raw exception code in order to only process
+	 * the trap if no SError is pending. We will come back to the
+	 * same PC once the SError has been injected, and replay the
+	 * trapping instruction.
+	 */
 	if (exit_code == ARM_EXCEPTION_TRAP && !__populate_fault_info(vcpu))
 		goto again;