On 30/08/2021 14:03, Jan Beulich wrote:
> Assuming that the accounting for IOMMU page tables will also take care
> of the P2M needs was wrong: dom0_paging_pages() can determine a far
> higher value, high enough for the system to run out of memory while
> setting up Dom0. Hence in the case of shared page tables the larger of
> the two values needs to be used (without shared page tables the sum of
> both continues to be applicable).
I'm afraid that I can't follow this at all.
What causes the system to run out of RAM while constructing dom0?
>
> While there also account for two further aspects in the PV case: With
> "iommu=dom0-passthrough" no IOMMU page tables would get allocated, so
> none need accounting for. And if shadow mode is to be enabled, setting
> aside a suitable amount for the P2M pool to get populated is also
> necessary (i.e. similar to the non-shared-page-tables case of PVH).
>
> Signed-off-by: Jan Beulich <jbeul...@suse.com>
>
> --- a/xen/arch/x86/dom0_build.c
> +++ b/xen/arch/x86/dom0_build.c
> @@ -318,7 +318,7 @@ unsigned long __init dom0_compute_nr_pag
> struct domain *d, struct elf_dom_parms *parms, unsigned long initrd_len)
> {
> nodeid_t node;
> - unsigned long avail = 0, nr_pages, min_pages, max_pages;
> + unsigned long avail = 0, nr_pages, min_pages, max_pages, iommu_pages = 0;
> bool need_paging;
>
> /* The ordering of operands is to work around a clang5 issue. */
> @@ -337,18 +337,23 @@ unsigned long __init dom0_compute_nr_pag
> avail -= d->max_vcpus - 1;
>
> /* Reserve memory for iommu_dom0_init() (rough estimate). */
> - if ( is_iommu_enabled(d) )
> + if ( is_iommu_enabled(d) && !iommu_hwdom_passthrough )
> {
> unsigned int s;
>
> for ( s = 9; s < BITS_PER_LONG; s += 9 )
> - avail -= max_pdx >> s;
> + iommu_pages += max_pdx >> s;
> +
> + avail -= iommu_pages;
> }
>
> - need_paging = is_hvm_domain(d) &&
> - (!iommu_use_hap_pt(d) || !paging_mode_hap(d));
> + need_paging = is_hvm_domain(d)
> + ? !iommu_use_hap_pt(d) || !paging_mode_hap(d)
> + : opt_dom0_shadow;
As per patch 4, this condition needs adjusting.
~Andrew
> for ( ; ; need_paging = false )
> {
> + unsigned long paging_pages;
> +
> nr_pages = get_memsize(&dom0_size, avail);
> min_pages = get_memsize(&dom0_min_size, avail);
> max_pages = get_memsize(&dom0_max_size, avail);
> @@ -377,11 +382,20 @@ unsigned long __init dom0_compute_nr_pag
> nr_pages = min(nr_pages, max_pages);
> nr_pages = min(nr_pages, avail);
>
> - if ( !need_paging )
> - break;
> + paging_pages = paging_mode_enabled(d) || need_paging
> + ? dom0_paging_pages(d, nr_pages) : 0;
>
> /* Reserve memory for shadow or HAP. */
> - avail -= dom0_paging_pages(d, nr_pages);
> + if ( !need_paging )
> + {
> + if ( paging_pages <= iommu_pages )
> + break;
> +
> + avail -= paging_pages - iommu_pages;
> + }
> + else
> + avail -= paging_pages;
> + iommu_pages = paging_pages;
> }
>
> if ( is_pv_domain(d) &&
>
