Commit a78986aa authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

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: default avatarAdam Borowski <kilobyte@angband.pl>
Analyzed-by: default avatarDavid Hildenbrand <david@redhat.com>
Acked-by: default avatarDan Williams <dan.j.williams@intel.com>
Cc: stable@vger.kernel.org
Fixes: 3565fce3 ("mm, x86: get_user_pages() for dax mappings")
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 29881b6e

arch/x86/kvm/mmu.c

+4 −4
Original line number Diff line number Diff line
@@ -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;
@@ -5914,8 +5914,8 @@ 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) &&

		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);

include/linux/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -966,6 +966,7 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu); 
void kvm_vcpu_kick(struct kvm_vcpu *vcpu);



bool kvm_is_reserved_pfn(kvm_pfn_t pfn);

bool kvm_is_zone_device_pfn(kvm_pfn_t pfn);



struct kvm_irq_ack_notifier {

	struct hlist_node link;

virt/kvm/kvm_main.c

+23 −3
Original line number Diff line number Diff line
@@ -149,10 +149,30 @@ __weak int kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm, 
	return 0;

}



bool kvm_is_zone_device_pfn(kvm_pfn_t pfn)

{

	/*

	 * The metadata used by is_zone_device_page() to determine whether or

	 * not a page is ZONE_DEVICE is guaranteed to be valid if and only if

	 * the device has been pinned, e.g. by get_user_pages().  WARN if the

	 * page_count() is zero to help detect bad usage of this helper.

	 */

	if (!pfn_valid(pfn) || WARN_ON_ONCE(!page_count(pfn_to_page(pfn))))

		return false;



	return is_zone_device_page(pfn_to_page(pfn));

}



bool kvm_is_reserved_pfn(kvm_pfn_t pfn)

{

	/*

	 * ZONE_DEVICE pages currently set PG_reserved, but from a refcounting

	 * perspective they are "normal" pages, albeit with slightly different

	 * usage rules.

	 */

	if (pfn_valid(pfn))

		return PageReserved(pfn_to_page(pfn));

		return PageReserved(pfn_to_page(pfn)) &&

		       !kvm_is_zone_device_pfn(pfn);



	return true;

}
@@ -1857,7 +1877,7 @@ EXPORT_SYMBOL_GPL(kvm_release_pfn_dirty); 


void kvm_set_pfn_dirty(kvm_pfn_t pfn)

{

	if (!kvm_is_reserved_pfn(pfn)) {

	if (!kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn)) {

		struct page *page = pfn_to_page(pfn);



		SetPageDirty(page);
@@ -1867,7 +1887,7 @@ EXPORT_SYMBOL_GPL(kvm_set_pfn_dirty); 


void kvm_set_pfn_accessed(kvm_pfn_t pfn)

{

	if (!kvm_is_reserved_pfn(pfn))

	if (!kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn))

		mark_page_accessed(pfn_to_page(pfn));

}

EXPORT_SYMBOL_GPL(kvm_set_pfn_accessed);

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