From: David Woodhouse dwmw@amazon.co.uk
commit 0985dba842eaa391858972cfe2724c3c174a2827 upstream.
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@vger.kernel.org Fixes: 40da8ccd724f ("KVM: x86/xen: Add event channel interrupt vector upcall") Signed-off-by: David Woodhouse dwmw@amazon.co.uk Message-Id: 168bf8c689561da904e48e2ff5ae4713eaef9e2d.camel@infradead.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/xen.c | 27 ++++++++++++++++++++++----- 1 file changed, 22 insertions(+), 5 deletions(-)
--- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -191,6 +191,7 @@ void kvm_xen_update_runstate_guest(struc
int __kvm_xen_has_interrupt(struct kvm_vcpu *v) { + int err; u8 rc = 0;
/* @@ -217,13 +218,29 @@ int __kvm_xen_has_interrupt(struct kvm_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; }