From: David Woodhouse <dwmw@xxxxxxxxxxxx>
In kvm_vcpu_block, the current task is set to TASK_INTERRUPTIBLE before
making a final check whether the vCPU should be woken from HLT by any
incoming interrupt.
This is a problem for the get_user() in __kvm_xen_has_interrupt(), which
really shouldn't be sleeping when the task state has already been set.
I think it's actually harmless as it would just manifest itself as a
spurious wakeup, but it's causing a debug warning:
[ 230.963649] do not call blocking ops when !TASK_RUNNING; state=1 set at [<00000000b6bcdbc9>] prepare_to_swait_exclusive+0x30/0x80
Fix the warning by turning it into an *explicit* spurious wakeup. When
invoked with !task_is_running(current) (and we might as well add
in_atomic() there while we're at it), just return 1 to indicate that
an IRQ is pending, which will cause a wakeup and then something will
call it again in a context that *can* sleep so it can fault the page
back in.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 40da8ccd724f ("KVM: x86/xen: Add event channel interrupt vector upcall")
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
arch/x86/kvm/xen.c | 27 ++++++++++++++++++++++-----
1 file changed, 22 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 9ea9c3dabe37..8f62baebd028 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -190,6 +190,7 @@ void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, int state)
int __kvm_xen_has_interrupt(struct kvm_vcpu *v)
{
+ int err;
u8 rc = 0;
/*
@@ -216,13 +217,29 @@ int __kvm_xen_has_interrupt(struct kvm_vcpu *v)
if (likely(slots->generation == ghc->generation &&
!kvm_is_error_hva(ghc->hva) && ghc->memslot)) {
/* Fast path */
- __get_user(rc, (u8 __user *)ghc->hva + offset);
- } else {
- /* Slow path */
- kvm_read_guest_offset_cached(v->kvm, ghc, &rc, offset,
- sizeof(rc));
+ pagefault_disable();
+ err = __get_user(rc, (u8 __user *)ghc->hva + offset);
+ pagefault_enable();
+ if (!err)
+ return rc;
}
+ /* Slow path */
+
+ /*
+ * This function gets called from kvm_vcpu_block() after setting the
+ * task to TASK_INTERRUPTIBLE, to see if it needs to wake immediately
+ * from a HLT. So we really mustn't sleep. If the page ended up absent
+ * at that point, just return 1 in order to trigger an immediate wake,
+ * and we'll end up getting called again from a context where we *can*
+ * fault in the page and wait for it.
+ */
+ if (in_atomic() || !task_is_running(current))
+ return 1;
+
+ kvm_read_guest_offset_cached(v->kvm, ghc, &rc, offset,
+ sizeof(rc));
+
return rc;
}
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