KVM: arm64: Stop handle_exit() from handling HVC twice when an SError occurs

Prior to commit 36727d4637b6 ("KVM: arm64: Move PC rollback on SError to
HYP"), when an SError is synchronised due to another exception, KVM
handles the SError first. If the guest survives, the instruction that
triggered the original exception is re-exectued to handle the first
exception. HVC is treated as a special case as the instruction wouldn't
normally be re-exectued, as its not a trap.

Commit 36727d4637b6 didn't preserve the behaviour of the 'return 1'
that skips the rest of handle_exit().

Since commit 36727d4637b6, KVM will try to handle the SError and the
original exception at the same time. When the exception was an HVC,
fixup_guest_exit() has already rolled back ELR_EL2, meaning if the
guest has virtual SError masked, it will execute and handle the HVC
twice.

Restore the original behaviour.

Fixes: 36727d4637b6 ("KVM: arm64: Move PC rollback on SError to HYP")
Cc: stable@vger.kernel.org
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220127122052.1584324-4-james.morse@arm.com

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index fd2dd26caf910287c005f109a3640e7980bfe442..e3140abd2e2eb3758e756457f0790361ba208a49 100644 (file)
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -228,6 +228,14 @@ int handle_exit(struct kvm_vcpu *vcpu, int exception_index)
 {
        struct kvm_run *run = vcpu->run;
 
+       if (ARM_SERROR_PENDING(exception_index)) {
+               /*
+                * The SError is handled by handle_exit_early(). If the guest
+                * survives it will re-execute the original instruction.
+                */
+               return 1;
+       }
+
        exception_index = ARM_EXCEPTION_CODE(exception_index);
 
        switch (exception_index) {