linux-kernel - [PATCH v6 4/4] KVM: mmu: remove over-aggressive warnings

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Message-Id: <20230330085802.2414466-5-stevensd@google.com>
Date:   Thu, 30 Mar 2023 17:58:02 +0900
From:   David Stevens <stevensd@...omium.org>
To:     Marc Zyngier <maz@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Oliver Upton <oliver.upton@...ux.dev>,
        Paolo Bonzini <pbonzini@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        David Stevens <stevensd@...omium.org>
Subject: [PATCH v6 4/4] KVM: mmu: remove over-aggressive warnings

From: David Stevens <stevensd@...omium.org>

Remove two warnings that require ref counts for pages to be non-zero, as
mapped pfns from follow_pfn may not have an initialized ref count.

Signed-off-by: David Stevens <stevensd@...omium.org>
---
 arch/x86/kvm/mmu/mmu.c | 10 ----------
 virt/kvm/kvm_main.c    |  5 ++---
 2 files changed, 2 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 86b74e7bccfa..46b3d6c0ff27 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -555,7 +555,6 @@ static u64 mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep)
 	kvm_pfn_t pfn;
 	u64 old_spte = *sptep;
 	int level = sptep_to_sp(sptep)->role.level;
-	struct page *page;
 
 	if (!is_shadow_present_pte(old_spte) ||
 	    !spte_has_volatile_bits(old_spte))
@@ -570,15 +569,6 @@ static u64 mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep)
 
 	pfn = spte_to_pfn(old_spte);
 
-	/*
-	 * KVM doesn't hold a reference to any pages mapped into the guest, and
-	 * instead uses the mmu_notifier to ensure that KVM unmaps any pages
-	 * before they are reclaimed.  Sanity check that, if the pfn is backed
-	 * by a refcounted page, the refcount is elevated.
-	 */
-	page = kvm_pfn_to_refcounted_page(pfn);
-	WARN_ON(page && !page_count(page));
-
 	if (is_accessed_spte(old_spte))
 		kvm_set_pfn_accessed(pfn);
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 007dd984eeea..a80070cb04d7 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -165,10 +165,9 @@ bool kvm_is_zone_device_page(struct page *page)
 	/*
 	 * 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.
+	 * the device has been pinned, e.g. by get_user_pages().
 	 */
-	if (WARN_ON_ONCE(!page_count(page)))
+	if (!page_count(page))
 		return false;
 
 	return is_zone_device_page(page);
-- 
2.40.0.348.gf938b09366-goog