linux-kernel - [PATCH v10 2/8] KVM: Relax BUG

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Date: Wed, 21 Feb 2024 16:25:20 +0900
From: David Stevens <stevensd@...omium.org>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Yu Zhang <yu.c.zhang@...ux.intel.com>,
	Isaku Yamahata <isaku.yamahata@...il.com>,
	Zhi Wang <zhi.wang.linux@...il.com>,
	Maxim Levitsky <mlevitsk@...hat.com>,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	David Stevens <stevensd@...omium.org>
Subject: [PATCH v10 2/8] KVM: Relax BUG_ON argument validation

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

hva_to_pfn() includes a check that KVM isn't trying to do an async page
fault in a situation where it can't sleep. Downgrade this check from a
BUG_ON() to a WARN_ON_ONCE(), since DoS'ing the guest (at worst) is
better than bringing down the host.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: David Stevens <stevensd@...omium.org>
---
 virt/kvm/kvm_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c5e4bf7c48f9..6f37d56fb2fc 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2979,7 +2979,7 @@ kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool interruptible,
 	int npages, r;
 
 	/* we can do it either atomically or asynchronously, not both */
-	BUG_ON(atomic && async);
+	WARN_ON_ONCE(atomic && async);
 
 	if (hva_to_pfn_fast(addr, write_fault, writable, &pfn))
 		return pfn;
-- 
2.44.0.rc0.258.g7320e95886-goog