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Re: [Xen-devel] [PATCH 1/4] mm: disallow MEMF_no_refcount to be passed for domain-owned allocations


  • To: Jan Beulich <JBeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Tue, 20 Nov 2018 16:35:06 +0000
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  • Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>
  • Delivery-date: Tue, 20 Nov 2018 16:48:53 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 20/11/2018 16:17, Jan Beulich wrote:
> When such pages get assigned to domains (and hence their ->tot_pages
> not incremented accordingly) we would otherwise also need to suppress
> decrementing the count when freeing those pages.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -2303,6 +2303,8 @@ struct page_info *alloc_domheap_pages(
>  
>      if ( memflags & MEMF_no_owner )
>          memflags |= MEMF_no_refcount;
> +    else if ( (memflags & MEMF_no_refcount) && d )
> +        return NULL;

Perhaps ASSERT_UNREACHABLE() in here as well?

As we've learnt the hard way, this is definitely a programming error, so
providing a stack trace is liable to be more helpful to someone
debugging why their memory allocations are suddenly failing.

~Andrew

>  
>      if ( dma_bitsize && ((dma_zone = bits_to_zone(dma_bitsize)) < zone_hi) )
>          pg = alloc_heap_pages(dma_zone + 1, zone_hi, order, memflags, d);
>
>


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