Re: [Xen-devel] [PATCH V2 1/2] x86/hvm: Add check when register io handler

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: suravee.suthikulpanit@xxxxxxx
> [mailto:suravee.suthikulpanit@xxxxxxx]
> Sent: 13 May 2016 20:37
> To: xen-devel@xxxxxxxxxxxxx; George Dunlap; jbeulich@xxxxxxxx
> Cc: Paul Durrant; Suravee Suthikulpanit; Suravee Suthikulpanit
> Subject: [PATCH V2 1/2] x86/hvm: Add check when register io handler
> 
> From: Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx>
> 
> At the time of registering HVM I/O handler, the HVM domain might
> not have been initialized,

I/O handler registration is internal to Xen so any caller that attempt to 
register before domain initialization should be removed and replaced with one 
that does it at the right time.

> which means the hvm_domain.io_handler
> would be NULL. In the hvm_next_io_handler(), this should be checked
> before returning and referencing the array. Also, the io_handler_count
> should only be incremented on success.
> 
> So, this patch adds error handling in hvm_next_io_handler.
> 

This isn't necessary. An ASSERT would be preferable so that buggy callers can 
be easily caught.

  Paul

> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> ---
>  xen/arch/x86/hvm/intercept.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/x86/hvm/intercept.c b/xen/arch/x86/hvm/intercept.c
> index 7096d74..b837f5f 100644
> --- a/xen/arch/x86/hvm/intercept.c
> +++ b/xen/arch/x86/hvm/intercept.c
> @@ -248,7 +248,10 @@ int hvm_io_intercept(ioreq_t *p)
> 
>  struct hvm_io_handler *hvm_next_io_handler(struct domain *d)
>  {
> -    unsigned int i = d->arch.hvm_domain.io_handler_count++;
> +    unsigned int i = d->arch.hvm_domain.io_handler_count;
> +
> +    if ( !d->arch.hvm_domain.io_handler )
> +        return NULL;
> 
>      if ( i == NR_IO_HANDLERS )
>      {
> @@ -256,6 +259,7 @@ struct hvm_io_handler *hvm_next_io_handler(struct
> domain *d)
>          return NULL;
>      }
> 
> +    d->arch.hvm_domain.io_handler_count++;
>      return &d->arch.hvm_domain.io_handler[i];
>  }
> 
> --
> 1.9.1


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