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[209.132.180.67]) by mx.google.com with ESMTP id h200si3329635oib.258.2019.12.12.08.55.50; Thu, 12 Dec 2019 08:56:03 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@intel-com.20150623.gappssmtp.com header.s=20150623 header.b=rgtrRVuq; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729930AbfLLQzL (ORCPT + 99 others); Thu, 12 Dec 2019 11:55:11 -0500 Received: from mail-ot1-f68.google.com ([209.85.210.68]:38687 "EHLO mail-ot1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729260AbfLLQzL (ORCPT ); Thu, 12 Dec 2019 11:55:11 -0500 Received: by mail-ot1-f68.google.com with SMTP id h20so2674116otn.5 for ; Thu, 12 Dec 2019 08:55:10 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=IjDUBfxBJhXNaC2BIeIEC43hkHaDAGwaiQqn3TQYiIk=; b=rgtrRVuq6mdTTp7elEykgE89Ca9kZfn8QGs2v++8uceH3hFUstkL2ayypXJmkZfxk1 iEGWW63b5xe8cb11bY30cimjn6zlRLLAZ0SBZbITIqWmtK9ObULY/ZUjOhVQpHgy43tK vac8DIrdJ543HRUPfBajdEIZV1GmYiBat32AFIvi3TBXKX1su2WzlK2cncw5h6144hey kOBYwgTRo2VfskCO21DnFQr6uUTKWUqlPo51785MVMk82ugVbKBZDUbGNO7frgqCR7rY ZjPZecmpJa3QOFc0keUDCp2aSgzufXIt1iNv04Rl7hV1xbkD7RXbi3OjPTdOoMLxaXhC B4+w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=IjDUBfxBJhXNaC2BIeIEC43hkHaDAGwaiQqn3TQYiIk=; b=eS27eYcIWZ5zhnPVidnc9vc8Fw1M9aX2j9qdv2r0OXU52PWnYQhoL1tvCZSuw7T0bq 36To9vxl2rQzYD7vYiObP4luwz7FGoWURZui8qgqFrWMKnBjDKBlYd1kaNcHo+X2S5QK hgm1QGWIT5fWDkw6ldVaI/8m1JL1seKH4jZbUwo+hQeO49s5xQDWJ7nJSuwCsNxGEG+8 wIsOATBPMqMnEbMksjbYrbHqgGuQW4RNuJtfhXageHGwZGaIw6eyiu5KZFGIi/5JZlz7 nbgmDqad6nojIJi8bRnkqVMfht23ecN0q490gKabFDTjrH7quaaSw6ctid09QwpZbJ6f ubDw== X-Gm-Message-State: APjAAAXiDYC6D0+ywJcBYeQrYDOy5QzQWyq3e57CHA/dJlu0n4djO4Vx 0RRVo2LbxX+tmbXwEYIwetxzzTGX3MoYeMYhp5JUkQ== X-Received: by 2002:a9d:4e99:: with SMTP id v25mr9361501otk.363.1576169710137; Thu, 12 Dec 2019 08:55:10 -0800 (PST) MIME-Version: 1.0 References: <20191211213207.215936-1-brho@google.com> <20191211213207.215936-3-brho@google.com> <376DB19A-4EF1-42BF-A73C-741558E397D4@oracle.com> In-Reply-To: <376DB19A-4EF1-42BF-A73C-741558E397D4@oracle.com> From: Dan Williams Date: Thu, 12 Dec 2019 08:54:59 -0800 Message-ID: Subject: Re: [PATCH v4 2/2] kvm: Use huge pages for DAX-backed files To: Liran Alon Cc: Barret Rhoden , Paolo Bonzini , David Hildenbrand , Dave Jiang , Alexander Duyck , linux-nvdimm , X86 ML , KVM list , Linux Kernel Mailing List , "Zeng, Jason" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 12, 2019 at 4:34 AM Liran Alon wrote: > > > > > On 11 Dec 2019, at 23:32, 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. > > 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->pa= gesize()=3D=3Dhugetlb_vm_op_pagesize(). > > Only for pages that were originally mapped as small-pages and later merge= d 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-ta= bles. 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 =E2=80=9Cstruct page=E2=80=9D of these pages should be modif= ied as usual to make PageTransCompound() return true for them. I=E2=80=99m = 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 = =E2=80=9Cstruct page=E2=80=9D 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 > > --- > > 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 p= fn) > > +{ > > + struct page *page =3D 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 alr= eady > > + * been mapped into the host-side page table during try_async_pf(= ), so > > + * we can check the page tables directly. > > + */ > > + hva =3D 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=E2=80=99t dev_pagemap_mapping_shift() get =E2=80=9Cstruct page=E2= =80=9D 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 kv= m_vcpu *vcpu, > > * here. > > */ > > if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) && > > - !kvm_is_zone_device_pfn(pfn) && level =3D=3D PT_PAGE_TABLE_LE= VEL && > > - PageTransCompoundMap(pfn_to_page(pfn)) && > > + level =3D=3D 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 k= vm *kvm, > > * mapping if the indirect sp has level =3D 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 > > >