Messages in this thread | | | Date | Wed, 17 Sep 2014 15:07:05 +0100 | From | David Vrabel <> | Subject | Re: [Xen-devel] [PATCH V2 3/3] xen: eliminate scalability issues from initial mapping setup |
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On 17/09/14 05:12, Juergen Gross wrote: > Direct Xen to place the initial P->M table outside of the initial > mapping, as otherwise the 1G (implementation) / 2G (theoretical) > restriction on the size of the initial mapping limits the amount > of memory a domain can be handed initially. > > As the initial P->M table is copied rather early during boot to > domain private memory and it's initial virtual mapping is dropped, > the easiest way to avoid virtual address conflicts with other > addresses in the kernel is to use a user address area for the > virtual address of the initial P->M table. This allows us to just > throw away the page tables of the initial mapping after the copy > without having to care about address invalidation.
This needs an additional paragraph like:
"This does not increase the amount of memory the guest can use. This is still limited to 512 GiB by the 3-level p2m."
> --- a/arch/x86/xen/mmu.c > +++ b/arch/x86/xen/mmu.c > @@ -1198,6 +1198,76 @@ static void __init xen_cleanhighmap(unsigned long vaddr, [...] > +/* > + * Since it is well isolated we can (and since it is perhaps large we should) > + * also free the page tables mapping the initial P->M table. > + */ > +static void __init xen_cleanmfnmap(unsigned long vaddr) > +{ > + unsigned long va = vaddr & PMD_MASK; > + unsigned long pa; > + pgd_t *pgd = pgd_offset_k(va); > + pud_t *pud_page = pud_offset(pgd, 0); > + pud_t *pud; > + pmd_t *pmd; > + pte_t *pte; > + unsigned int i; > + > + set_pgd(pgd, __pgd(0)); > + do { > + pud = pud_page + pud_index(va); > + if (pud_none(*pud)) { > + va += PUD_SIZE; > + } else if (pud_large(*pud)) { > + pa = pud_val(*pud) & PHYSICAL_PAGE_MASK; > + xen_free_ro_pages(pa, PUD_SIZE); > + va += PUD_SIZE;
Are you missing a ClearPagePinned(..) here?
> + } else { > + pmd = pmd_offset(pud, va); > + if (pmd_large(*pmd)) { > + pa = pmd_val(*pmd) & PHYSICAL_PAGE_MASK; > + xen_free_ro_pages(pa, PMD_SIZE); > + } else if (!pmd_none(*pmd)) { > + pte = pte_offset_kernel(pmd, va); > + for (i = 0; i < PTRS_PER_PTE; ++i) { > + if (pte_none(pte[i])) > + break; > + pa = pte_pfn(pte[i]) << PAGE_SHIFT; > + xen_free_ro_pages(pa, PAGE_SIZE); > + }
> + pa = __pa(pte) & PHYSICAL_PAGE_MASK; > + ClearPagePinned(virt_to_page(__va(pa))); > + xen_free_ro_pages(pa, PAGE_SIZE);
Put this into a helper function? It's used here...
> + } > + va += PMD_SIZE; > + if (pmd_index(va)) > + continue; > + pa = __pa(pmd) & PHYSICAL_PAGE_MASK; > + ClearPagePinned(virt_to_page(__va(pa))); > + xen_free_ro_pages(pa, PAGE_SIZE);
...and here...
> + } > + > + } while (pud_index(va) || pmd_index(va)); > + pa = __pa(pud_page) & PHYSICAL_PAGE_MASK; > + ClearPagePinned(virt_to_page(__va(pa))); > + xen_free_ro_pages(pa, PAGE_SIZE);
... and here.
> @@ -1529,6 +1604,22 @@ static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte) > #else /* CONFIG_X86_64 */ > static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte) > { > + unsigned long pfn; > + > + if (xen_feature(XENFEAT_writable_page_tables) || > + xen_feature(XENFEAT_auto_translated_physmap) || > + xen_start_info->mfn_list >= __START_KERNEL_map) > + return pte; > + > + /* > + * Pages belonging to the initial p2m list mapped outside the default > + * address range must be mapped read-only.
Why? I didn't think was anything special about these MFNs.
David
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