Re: [Xen-ia64-devel] [PATCH] Fix a bug in xencomm_copy_from/to_guest()

[SUZUKI Kazuhiro <kaz@xxxxxxxxxxxxxx>]

Hi Isaku,

Thank you for your comment.
It seems good. I think that your patch is better.

Thanks,
KAZ


From: Isaku Yamahata <yamahata@xxxxxxxxxxxxx>
Subject: Re: [Xen-ia64-devel] [PATCH] Fix a bug in xencomm_copy_from/to_guest()
Date: Wed, 27 Dec 2006 19:16:16 +0900

> 
> Hi Kaz.
> 
> On Wed, Dec 27, 2006 at 06:27:26PM +0900, SUZUKI Kazuhiro wrote:
> > diff -r 80c5b5914b79 xen/arch/ia64/xen/xencomm.c
> > --- a/xen/arch/ia64/xen/xencomm.c   Wed Dec 20 14:55:02 2006 -0700
> > +++ b/xen/arch/ia64/xen/xencomm.c   Wed Dec 27 18:03:10 2006 +0900
> > @@ -148,6 +148,13 @@ xencomm_copy_from_guest(
> >          pgoffset = src_paddr % PAGE_SIZE;
> >          chunksz = PAGE_SIZE - pgoffset;
> >  
> > +        if (chunksz <= skip) {
> > +            from_pos += chunksz;
> > +            skip -= chunksz;
> > +            i++;
> > +            continue;
> > +        }
> > +
> >          chunk_skip = min(chunksz, skip);
> >          from_pos += chunk_skip;
> >          chunksz -= chunk_skip;
> 
> This condition looks odd.
> I guess the issues which you've seen is 
> calling xencomm_copy_chunk_{to, from} with len = 0.
> (If I'm wrong, correct me.)
> The patch should looks like as follows.
> And xen/common/xencomm.c should modified similary too.
> 
> --- xen/arch/ia64/xen/xencomm.c   2006-12-21 12:05:05.000000000 +0900
> +++ xen/arch/ia64/xen/xencomm.c.new       2006-12-27 19:12:19.000000000 +0900
> @@ -153,7 +153,7 @@ xencomm_copy_from_guest(
>          chunksz -= chunk_skip;
>          skip -= chunk_skip;
>  
> -        if (skip == 0) {
> +        if (skip == 0 && chunksz > 0) {
>              unsigned int bytes = min(chunksz, n - to_pos);
>             int res;
>  
> @@ -295,7 +295,7 @@ xencomm_copy_to_guest(
>          skip -= chunk_skip;
>          dest_paddr += chunk_skip;
>  
> -        if (skip == 0) {
> +        if (skip == 0 && chunksz > 0) {
>              unsigned int bytes = min(chunksz, n - from_pos);
>              int res;
> -- 
> yamahata

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