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arm64: hyp/kvm: Make hyp-stub reject kvm_call_hyp()

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A later patch implements kvm_arch_hardware_disable(), to remove kvm
from el2, and re-instate the hyp-stub.

This can happen while guests are running, particularly when kvm_reboot()
calls kvm_arch_hardware_disable() on each cpu. This can interrupt a guest,
remove kvm, then allow the guest to be scheduled again. This causes
kvm_call_hyp() to be run against the hyp-stub.

Change the hyp-stub to return a new exception type when this happens,
and add code to kvm's handle_exit() to tell userspace we failed to
enter the guest.

Signed-off-by: James Morse <james.morse@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
James Morse 2016-04-27 17:47:04 +01:00 committed by Will Deacon
parent ad72e59ff2
commit c94b0cf282
3 changed files with 12 additions and 2 deletions
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2
arch/arm64/include/asm/kvm_asm.h
View File

@ -22,6 +22,8 @@
#define ARM_EXCEPTION_IRQ 0
#define ARM_EXCEPTION_TRAP 1
/* The hyp-stub will return this for any kvm_call_hyp() call */
#define ARM_EXCEPTION_HYP_GONE 2
#define KVM_ARM64_DEBUG_DIRTY_SHIFT 0
#define KVM_ARM64_DEBUG_DIRTY (1 << KVM_ARM64_DEBUG_DIRTY_SHIFT)

5
arch/arm64/kernel/hyp-stub.S
View File

@ -23,6 +23,7 @@
#include <asm/assembler.h>
#include <asm/kvm_arm.h>
#include <asm/kvm_asm.h>
#include <asm/ptrace.h>
#include <asm/virt.h>
@ -70,8 +71,8 @@ el1_sync:
msr vbar_el2, x1
b 9f
/* Unrecognised call type */
2: mov x0, xzr
/* Someone called kvm_call_hyp() against the hyp-stub... */
2: mov x0, #ARM_EXCEPTION_HYP_GONE
9: eret
ENDPROC(el1_sync)

7
arch/arm64/kvm/handle_exit.c
View File

@ -186,6 +186,13 @@ int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
exit_handler = kvm_get_exit_handler(vcpu);
return exit_handler(vcpu, run);
case ARM_EXCEPTION_HYP_GONE:
/*
* EL2 has been reset to the hyp-stub. This happens when a guest
* is pre-empted by kvm_reboot()'s shutdown call.
*/
run->exit_reason = KVM_EXIT_FAIL_ENTRY;
return 0;
default:
kvm_pr_unimpl("Unsupported exception type: %d",
exception_index);