On 13/11/2018 11:02, Pankaj Gupta wrote: > >> >> On 09.11.18 21:39, Barret Rhoden 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. >>> >>> Note that KVM already faulted in the page (or huge page) in the host's >>> page table, and we hold the KVM mmu spinlock (grabbed before checking >>> the mmu seq). >> >> I wonder if the KVM mmu spinlock is enough for walking (not KVM >> exclusive) host page tables. Can you elaborate? > > As this patch is dependent on PageReserved patch(which is in progress), just > wondering if we are able to test the code path for hugepage with DAX.
The MMU spinlock is taken in kvm_mmu_notifier_invalidate_range_end, so it should be enough. Paolo > > Thanks, > Pankaj > >> >>> >>> Signed-off-by: Barret Rhoden <[email protected]> >>> --- >>> arch/x86/kvm/mmu.c | 34 ++++++++++++++++++++++++++++++++-- >>> 1 file changed, 32 insertions(+), 2 deletions(-) >>> >>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >>> index cf5f572f2305..2df8c459dc6a 100644 >>> --- a/arch/x86/kvm/mmu.c >>> +++ b/arch/x86/kvm/mmu.c >>> @@ -3152,6 +3152,36 @@ 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, map_shift; >>> + >>> + 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. >>> + */ >>> + map_shift = dev_pagemap_mapping_shift(hva, current->mm); >> >> You could get rid of that local variable map_shift. >> >>> + switch (map_shift) { >>> + case PMD_SHIFT: >>> + case PUD_SIZE: >>> + return true; >>> + } >>> + return false; >>> +} >>> + >>> static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu, >>> gfn_t *gfnp, kvm_pfn_t *pfnp, >>> int *levelp) >>> @@ -3168,7 +3198,7 @@ static void transparent_hugepage_adjust(struct >>> kvm_vcpu *vcpu, >>> */ >>> if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) && >>> level == PT_PAGE_TABLE_LEVEL && >>> - PageTransCompoundMap(pfn_to_page(pfn)) && >>> + pfn_is_huge_mapped(vcpu->kvm, gfn, pfn) && >>> !mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL)) { >>> unsigned long mask; >>> /* >>> @@ -5678,7 +5708,7 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm >>> *kvm, >>> */ >>> if (sp->role.direct && >>> !kvm_is_reserved_pfn(pfn) && >>> - PageTransCompoundMap(pfn_to_page(pfn))) { >>> + pfn_is_huge_mapped(kvm, sp->gfn, pfn)) { >>> pte_list_remove(rmap_head, sptep); >>> need_tlb_flush = 1; >>> goto restart; >>> >> >> This looks surprisingly simple to me :) >> >> -- >> >> Thanks, >> >> David / dhildenb >> _______________________________________________ Linux-nvdimm mailing list [email protected] https://lists.01.org/mailman/listinfo/linux-nvdimm
