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Commit 395ea79e authored by Marc Zyngier's avatar Marc Zyngier Committed by Christoffer Dall
Browse files

arm64: KVM: Handle async aborts delivered while at EL2 



If EL1 generates an asynchronous abort and then traps into EL2
before the abort has been delivered, we may end-up with the
abort firing at the worse possible place: on the host.

In order to avoid this, it is necessary to take the abort at EL2,
by clearing the PSTATE.A bit. In order to survive this abort,
we do it at a point where we're in a known state with respect
to the world switch, and handle the resulting exception,
overloading the exit code in the process.

Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
parent ddb3d07c

arch/arm64/kvm/hyp/entry.S

+32 −1
Original line number Diff line number Diff line
@@ -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)

arch/arm64/kvm/hyp/hyp-entry.S

+23 −2
Original line number Diff line number Diff line
@@ -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

arch/arm64/kvm/hyp/switch.c

+6 −0
Original line number Diff line number Diff line
@@ -292,6 +292,12 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu) 
	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;