[PATCH 14/14] KVM: x86/mmu: Use huge pages for DAX-backed files

From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Paul Mackerras <paulus@ozlabs.org>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	kvm-ppc@vger.kernel.org, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu,
	syzbot+c9d1fb51ac9d0d10c39d@syzkaller.appspotmail.com,
	Andrea Arcangeli <aarcange@redhat.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Barret Rhoden <brho@google.com>,
	David Hildenbrand <david@redhat.com>,
	Jason Zeng <jason.zeng@intel.com>,
	Dave Jiang <dave.jiang@intel.com>,
	Liran Alon <liran.alon@oracle.com>,
	linux-nvdimm <linux-nvdimm@lists.01.org>
Subject: [PATCH 14/14] KVM: x86/mmu: Use huge pages for DAX-backed files
Date: Wed,  8 Jan 2020 12:24:48 -0800	[thread overview]
Message-ID: <20200108202448.9669-15-sean.j.christopherson@intel.com> (raw)
In-Reply-To: <20200108202448.9669-1-sean.j.christopherson@intel.com>

Walk the host page tables to identify hugepage mappings for ZONE_DEVICE
pfns, i.e. DAX pages.  Explicitly query kvm_is_zone_device_pfn() when
deciding whether or not to bother walking the host page tables, as DAX
pages do not set up the head/tail infrastructure, i.e. will return false
for PageCompound() even when using huge pages.

Zap ZONE_DEVICE sptes when disabling dirty logging, e.g. if live
migration fails, to allow KVM to rebuild large pages for DAX-based
mappings.  Presumably DAX favors large pages, and worst case scenario is
a minor performance hit as KVM will need to re-fault all DAX-based
pages.

Suggested-by: Barret Rhoden <brho@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jason Zeng <jason.zeng@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Liran Alon <liran.alon@oracle.com>
Cc: linux-nvdimm <linux-nvdimm@lists.01.org>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/mmu/mmu.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 1e4e0ac169a7..324e1919722f 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3250,7 +3250,7 @@ static int host_pfn_mapping_level(struct kvm_vcpu *vcpu, gfn_t gfn,
 		     PT_DIRECTORY_LEVEL != (int)PG_LEVEL_2M ||
 		     PT_PDPE_LEVEL != (int)PG_LEVEL_1G);
 
-	if (!PageCompound(pfn_to_page(pfn)))
+	if (!PageCompound(pfn_to_page(pfn)) && !kvm_is_zone_device_pfn(pfn))
 		return PT_PAGE_TABLE_LEVEL;
 
 	/*
@@ -3282,8 +3282,7 @@ static int kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, gfn_t gfn,
 	if (unlikely(max_level == PT_PAGE_TABLE_LEVEL))
 		return PT_PAGE_TABLE_LEVEL;
 
-	if (is_error_noslot_pfn(pfn) || kvm_is_reserved_pfn(pfn) ||
-	    kvm_is_zone_device_pfn(pfn))
+	if (is_error_noslot_pfn(pfn) || kvm_is_reserved_pfn(pfn))
 		return PT_PAGE_TABLE_LEVEL;
 
 	slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
@@ -5910,8 +5909,8 @@ 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) &&
-		    PageCompound(pfn_to_page(pfn))) {
+		    (kvm_is_zone_device_pfn(pfn) ||
+		     PageCompound(pfn_to_page(pfn)))) {
 			pte_list_remove(rmap_head, sptep);
 
 			if (kvm_available_flush_tlb_with_range())
-- 
2.24.1

