linux-kernel - [PATCH v2 5/5] KVM: mmu: remove over-aggressive warnings

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Message-Id: <20210625073616.2184426-6-stevensd@google.com>
Date:   Fri, 25 Jun 2021 16:36:16 +0900
From:   David Stevens <stevensd@...omium.org>
To:     Marc Zyngier <maz@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Nick Piggin <npiggin@...il.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Will Deacon <will@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        kvm@...r.kernel.org, kvm-ppc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        David Stevens <stevensd@...omium.org>
Subject: [PATCH v2 5/5] 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 | 7 -------
 virt/kvm/kvm_main.c    | 2 +-
 2 files changed, 1 insertion(+), 8 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index dd5cb6e33591..0c47245594c6 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -607,13 +607,6 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
 
 	pfn = spte_to_pfn(old_spte);
 
-	/*
-	 * KVM does not hold the refcount of the page used by
-	 * kvm mmu, before reclaiming the page, we should
-	 * unmap it from mmu first.
-	 */
-	WARN_ON(!kvm_is_reserved_pfn(pfn) && !page_count(pfn_to_page(pfn)));
-
 	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 1de8702845ac..ce7126bab4b0 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -168,7 +168,7 @@ bool kvm_is_zone_device_pfn(kvm_pfn_t pfn)
 	 * 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))))
+	if (!pfn_valid(pfn) || !page_count(pfn_to_page(pfn)))
 		return false;
 
 	return is_zone_device_page(pfn_to_page(pfn));
-- 
2.32.0.93.g670b81a890-goog