From a78986aae9b2988f8493f9f65a587ee433e83bc3 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Mon, 11 Nov 2019 14:12:27 -0800 Subject: KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved Explicitly exempt ZONE_DEVICE pages from kvm_is_reserved_pfn() and instead manually handle ZONE_DEVICE on a case-by-case basis. For things like page refcounts, KVM needs to treat ZONE_DEVICE pages like normal pages, e.g. put pages grabbed via gup(). But for flows such as setting A/D bits or shifting refcounts for transparent huge pages, KVM needs to to avoid processing ZONE_DEVICE pages as the flows in question lack the underlying machinery for proper handling of ZONE_DEVICE pages. This fixes a hang reported by Adam Borowski[*] in dev_pagemap_cleanup() when running a KVM guest backed with /dev/dax memory, as KVM straight up doesn't put any references to ZONE_DEVICE pages acquired by gup(). Note, Dan Williams proposed an alternative solution of doing put_page() on ZONE_DEVICE pages immediately after gup() in order to simplify the auditing needed to ensure is_zone_device_page() is called if and only if the backing device is pinned (via gup()). But that approach would break kvm_vcpu_{un}map() as KVM requires the page to be pinned from map() 'til unmap() when accessing guest memory, unlike KVM's secondary MMU, which coordinates with mmu_notifier invalidations to avoid creating stale page references, i.e. doesn't rely on pages being pinned. [*] http://lkml.kernel.org/r/20190919115547.GA17963@angband.pl Reported-by: Adam Borowski Analyzed-by: David Hildenbrand Acked-by: Dan Williams Cc: stable@vger.kernel.org Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") Signed-off-by: Sean Christopherson Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'arch/x86/kvm/mmu.c') diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 24c23c66b226..bf82b1f2e834 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -3306,7 +3306,7 @@ static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu, * here. */ if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) && - level == PT_PAGE_TABLE_LEVEL && + !kvm_is_zone_device_pfn(pfn) && level == PT_PAGE_TABLE_LEVEL && PageTransCompoundMap(pfn_to_page(pfn)) && !mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL)) { unsigned long mask; @@ -5914,9 +5914,9 @@ restart: * the guest, and the guest page table is using 4K page size * mapping if the indirect sp has level = 1. */ - if (sp->role.direct && - !kvm_is_reserved_pfn(pfn) && - PageTransCompoundMap(pfn_to_page(pfn))) { + if (sp->role.direct && !kvm_is_reserved_pfn(pfn) && + !kvm_is_zone_device_pfn(pfn) && + PageTransCompoundMap(pfn_to_page(pfn))) { pte_list_remove(rmap_head, sptep); if (kvm_available_flush_tlb_with_range()) -- cgit