Re: [Xen-devel] xen/pvh linux: Use ballooning to allocate grant table pages

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Thu, 7 Feb 2013 13:54:25 +0300
Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:

> Hello Mukesh Rathor,
> 
> The patch 40f633eb0def: "xen/pvh linux: Use ballooning to allocate
> grant table pages" from Jan 31, 2013, leads to the following Sparse
> warning: "drivers/xen/grant-table.c:1095:28: error: bad constant
>       expression"
> 
> drivers/xen/grant-table.c
>   1092  static int xlated_setup_gnttab_pages(int numpages, void
> **addr) 1093  {
>   1094          int i, rc;
>   1095          unsigned long pfns[numpages];
>   1096          struct page *pages[numpages];
>                                    ^^^^^^^^
> Because the kernel uses an 8k stack if this is over 500 it will cause
> a kernel crash.  It will crash before we reach 500 actually.  It looks
> like typical values for this are around 4 so we're probably safe, but
> it's still a bit nasty.
> 
>   1097  
>   1098          rc = alloc_xenballooned_pages(numpages, pages, 0);
>   1099          if (rc != 0) {
>   1100                  pr_warn("%s Could not balloon alloc %d pfns
> rc:%d\n", __func__,
> 
> regards,
> dan carpenter

Hi Dan,

Yeah, I know. Currently, there is a hard max on num of grant pages to
32, but on average are lot less. So I think it should be OK. Konrad, do
you still want me to change it to kmalloc?

Thanks
Mukesh

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