linux-kernel - [PATCH 4/5] KVM: x86: change kvm_mmu_page_get_gfn BUG_ON to WARN

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Message-Id: <20190704093256.12989-5-pbonzini@redhat.com>
Date:   Thu,  4 Jul 2019 11:32:55 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     sean.j.christopherson@...el.com, vkuznets@...hat.com
Subject: [PATCH 4/5] KVM: x86: change kvm_mmu_page_get_gfn BUG_ON to WARN_ON

Note that in such a case it is quite likely that KVM will BUG_ON
in __pte_list_remove when the VM is closed.  However, there is no
immediate risk of memory corruption in the host so a WARN_ON is
enough and it lets you gather traces for debugging.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/mmu.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 084c1a0d9f98..0629a89bb070 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1098,10 +1098,16 @@ static gfn_t kvm_mmu_page_get_gfn(struct kvm_mmu_page *sp, int index)
 
 static void kvm_mmu_page_set_gfn(struct kvm_mmu_page *sp, int index, gfn_t gfn)
 {
-	if (sp->role.direct)
-		BUG_ON(gfn != kvm_mmu_page_get_gfn(sp, index));
-	else
+	if (!sp->role.direct) {
 		sp->gfns[index] = gfn;
+		return;
+	}
+
+	if (WARN_ON(gfn != kvm_mmu_page_get_gfn(sp, index)))
+		pr_err_ratelimited("gfn mismatch under direct page %llx "
+				   "(expected %llx, got %llx)\n",
+				   sp->gfn,
+				   kvm_mmu_page_get_gfn(sp, index), gfn);
 }
 
 /*
-- 
2.21.0