Re: [Xen-devel] [PATCH for-4.5] x86/hvm: do not create ioreq server if guest domain is dying

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx]
> Sent: 26 September 2014 13:23
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Paul Durrant; Ian Campbell; Jan Beulich; Andrew Jones
> Subject: [PATCH for-4.5] x86/hvm: do not create ioreq server if guest domain
> is dying
> 
> If HVM_PARAM_IOREQ_PFN, HVM_PARAM_BUFIOREQ_PFN, or
> HVM_PARAM_BUFIOREQ_EVTCHN
> parameters are read when guest domain is dying it leads to the following
> ASSERT:
> 
> (XEN) Assertion '_raw_spin_is_locked(lock)' failed at
> ...workspace/KERNEL/xen/xen/include/asm/spinlock.h:18
> (XEN) ----[ Xen-4.5-unstable  x86_64  debug=y  Not tainted ]----
> ...
> (XEN) Xen call trace:
> (XEN)    [<ffff82d08012b07f>] _spin_unlock+0x27/0x30
> (XEN)    [<ffff82d0801b6103>] hvm_create_ioreq_server+0x3df/0x49a
> (XEN)    [<ffff82d0801bcceb>] do_hvm_op+0x12bf/0x27a0
> (XEN)    [<ffff82d08022b9bb>] syscall_enter+0xeb/0x145
> 
> It doesn't make sense (and is unsafe) to create ioreq server if we're dying.
> Make
> hvm_create_ioreq_server() fail with -EFAULT in this case.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
>  xen/arch/x86/hvm/hvm.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 0a20cbe..2cc6de7 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -1038,6 +1038,9 @@ static int hvm_create_ioreq_server(struct domain
> *d, domid_t domid,
>      struct hvm_ioreq_server *s;
>      int rc;
> 
> +    if ( d->is_dying )
> +        return -EFAULT;
> +

Whilst I agree that it makes no sense to be creating in ioreq server in this 
case, this patch is not an actual fix for the bug.

The bug AFAICT is actually a stray spin_unlock() in the fail1 error case in 
hvm_ioreq_server_init().

  Paul

>      rc = -ENOMEM;
>      s = xzalloc(struct hvm_ioreq_server);
>      if ( !s )
> --
> 1.9.3


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