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Re: [Xen-devel] [PATCH v2 07/20] x86/mem_sharing: don't try to unshare twice during page fault


  • To: Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Thu, 19 Dec 2019 19:19:34 +0000
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  • Cc: Wei Liu <wl@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Thu, 19 Dec 2019 19:20:12 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 18/12/2019 19:40, Tamas K Lengyel wrote:
> @@ -1959,19 +1965,21 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned 
> long gla,
>       */
>      if ( paged )
>          p2m_mem_paging_populate(currd, gfn);
> +
> +#ifdef CONFIG_MEM_SHARING
>      if ( sharing_enomem )
>      {
> -        int rv;
> -
> -        if ( (rv = mem_sharing_notify_enomem(currd, gfn, true)) < 0 )
> +        if ( !vm_event_check_ring(currd->vm_event_share) )
>          {
>              gdprintk(XENLOG_ERR, "Domain %hu attempt to unshare "
> -                     "gfn %lx, ENOMEM and no helper (rc %d)\n",
> -                     currd->domain_id, gfn, rv);
> +                     "gfn %lx, ENOMEM and no helper\n",
> +                     currd->domain_id, gfn);

As observations on this and later patches.  Use %pd (gets d%u or d[NAME]
as applicable), especially were d[COW] is a liable domid to get.

Also, any action which crashes a domain must not be a gdprintk(),
because otherwise you end up with a domain_crash() and no
context/symptoms in release builds of Xen.

~Andrew

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