Re: [Xen-devel] PVH dom0 memory setup

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 09/08/2017 01:11 PM, Roger Pau Monné wrote:
> On Fri, Sep 08, 2017 at 10:56:33AM -0400, Boris Ostrovsky wrote:
>> I am slightly confused by the use of 'need_paging' variable in
>> dom0_compute_nr_pages().
>>
>> Because paging_mode_hap() and iommu_hap_pt_share are (almost?) always
>> true, we are not reducing available memory for PVH dom0 by page tables
>> size. But then in pvh_setup_p2m() we do use this memory by
>> paging_set_allocation(). And from what I've seen we then may run our of
>> heap pages when populating memory map (in the 'for' loop below).
>>
>> Am I not reading this correctly?
> Yes, I think you are reading this correctly. dom0_compute_nr_pages
> should set need_paging if the domain type is hvm AFAICT, because hap
> also consumes memory for it's page tables. Do you have a reliable way
> to trigger this?
>
> I was thinking of a fix along the lines of:

Yes, this is essentially what I ended up doing and yes it does fix this
problem.

I wasn't sure whether this would work for !HAP case (which we still
support).

-boris


>
> ---8<---
> diff --git a/xen/arch/x86/dom0_build.c b/xen/arch/x86/dom0_build.c
> index f616b99ddc..424192a7c4 100644
> --- a/xen/arch/x86/dom0_build.c
> +++ b/xen/arch/x86/dom0_build.c
> @@ -263,8 +263,7 @@ unsigned long __init dom0_compute_nr_pages(
>              avail -= max_pdx >> s;
>      }
>  
> -    need_paging = is_hvm_domain(d) &&
> -        (!iommu_hap_pt_share || !paging_mode_hap(d));
> +    need_paging = is_hvm_domain(d);
>      for ( ; ; need_paging = false )
>      {
>          nr_pages = dom0_nrpages;
>


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