On Thu, Dec 12, 2019 at 4:34 AM Liran Alon <[email protected]> wrote: > > > > > On 11 Dec 2019, at 23:32, Barret Rhoden <[email protected]> wrote: > > > > This change allows KVM to map DAX-backed files made of huge pages with > > huge mappings in the EPT/TDP. > > > > DAX pages are not PageTransCompound. The existing check is trying to > > determine if the mapping for the pfn is a huge mapping or not. For > > non-DAX maps, e.g. hugetlbfs, that means checking PageTransCompound. > > For DAX, we can check the page table itself. > > For hugetlbfs pages, tdp_page_fault() -> mapping_level() -> > host_mapping_level() -> kvm_host_page_size() -> vma_kernel_pagesize() > will return the page-size of the hugetlbfs without the need to parse the > page-tables. > See vma->vm_ops->pagesize() callback implementation at > hugetlb_vm_ops->pagesize()==hugetlb_vm_op_pagesize(). > > Only for pages that were originally mapped as small-pages and later merged to > larger pages by THP, there is a need to check for PageTransCompound(). Again, > instead of parsing page-tables. > > Therefore, it seems more logical to me that: > (a) If DAX-backed files are mapped as large-pages to userspace, it should be > reflected in vma->vm_ops->page_size() of that mapping. Causing > kvm_host_page_size() to return the right size without the need to parse the > page-tables.
A given dax-mapped vma may have mixed page sizes so ->page_size() can't be used reliably to enumerating the mapping size. > (b) If DAX-backed files small-pages can be later merged to large-pages by > THP, then the “struct page” of these pages should be modified as usual to > make PageTransCompound() return true for them. I’m not highly familiar with > this mechanism, but I would expect THP to be able to merge DAX-backed files > small-pages to large-pages in case DAX provides “struct page” for the DAX > pages. DAX pages do not participate in THP and do not have the PageTransCompound accounting. The only mechanism that records the mapping size for dax is the page tables themselves. > > > > > Note that KVM already faulted in the page (or huge page) in the host's > > page table, and we hold the KVM mmu spinlock. We grabbed that lock in > > kvm_mmu_notifier_invalidate_range_end, before checking the mmu seq. > > > > Signed-off-by: Barret Rhoden <[email protected]> > > --- > > arch/x86/kvm/mmu/mmu.c | 36 ++++++++++++++++++++++++++++++++---- > > 1 file changed, 32 insertions(+), 4 deletions(-) > > > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > > index 6f92b40d798c..cd07bc4e595f 100644 > > --- a/arch/x86/kvm/mmu/mmu.c > > +++ b/arch/x86/kvm/mmu/mmu.c > > @@ -3384,6 +3384,35 @@ static int kvm_handle_bad_page(struct kvm_vcpu > > *vcpu, gfn_t gfn, kvm_pfn_t pfn) > > return -EFAULT; > > } > > > > +static bool pfn_is_huge_mapped(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn) > > +{ > > + struct page *page = pfn_to_page(pfn); > > + unsigned long hva; > > + > > + if (!is_zone_device_page(page)) > > + return PageTransCompoundMap(page); > > + > > + /* > > + * DAX pages do not use compound pages. The page should have already > > + * been mapped into the host-side page table during try_async_pf(), so > > + * we can check the page tables directly. > > + */ > > + hva = gfn_to_hva(kvm, gfn); > > + if (kvm_is_error_hva(hva)) > > + return false; > > + > > + /* > > + * Our caller grabbed the KVM mmu_lock with a successful > > + * mmu_notifier_retry, so we're safe to walk the page table. > > + */ > > + switch (dev_pagemap_mapping_shift(hva, current->mm)) { > > Doesn’t dev_pagemap_mapping_shift() get “struct page” as first parameter? > Was this changed by a commit I missed? > > -Liran > > > + case PMD_SHIFT: > > + case PUD_SIZE: > > + return true; > > + } > > + return false; > > +} > > + > > static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu, > > gfn_t gfn, kvm_pfn_t *pfnp, > > int *levelp) > > @@ -3398,8 +3427,8 @@ static void transparent_hugepage_adjust(struct > > kvm_vcpu *vcpu, > > * here. > > */ > > if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) && > > - !kvm_is_zone_device_pfn(pfn) && level == PT_PAGE_TABLE_LEVEL && > > - PageTransCompoundMap(pfn_to_page(pfn)) && > > + level == PT_PAGE_TABLE_LEVEL && > > + pfn_is_huge_mapped(vcpu->kvm, gfn, pfn) && > > !mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL)) { > > unsigned long mask; > > /* > > @@ -6015,8 +6044,7 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm > > *kvm, > > * mapping if the indirect sp has level = 1. > > */ > > if (sp->role.direct && !kvm_is_reserved_pfn(pfn) && > > - !kvm_is_zone_device_pfn(pfn) && > > - PageTransCompoundMap(pfn_to_page(pfn))) { > > + pfn_is_huge_mapped(kvm, sp->gfn, pfn)) { > > pte_list_remove(rmap_head, sptep); > > > > if (kvm_available_flush_tlb_with_range()) > > -- > > 2.24.0.525.g8f36a354ae-goog > > > _______________________________________________ Linux-nvdimm mailing list -- [email protected] To unsubscribe send an email to [email protected]
