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From: David Hildenbrand <david@redhat.com>
To: "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	Igor Mammedov <imammedo@redhat.com>,
	Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Huacai Chen <chenhuacai@kernel.org>,
	Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
	Paul Mackerras <paulus@ozlabs.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	Cornelia Huck <cohuck@redhat.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 06/13] KVM: Move WARN on invalid memslot index to update_memslots()
Date: Wed, 18 Aug 2021 16:35:33 +0200	[thread overview]
Message-ID: <957c6b3d-9621-a5a5-418c-f61f87a32ee0@redhat.com> (raw)
In-Reply-To: <8db0f1d1901768b5de1417caa425e62d1118e5e8.1628871413.git.maciej.szmigiero@oracle.com>

On 13.08.21 21:33, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
> 
> Since kvm_memslot_move_forward() can theoretically return a negative
> memslot index even when kvm_memslot_move_backward() returned a positive one
> (and so did not WARN) let's just move the warning to the common code.
> 
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> ---
>   virt/kvm/kvm_main.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 03ef42d2e421..7000efff1425 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1293,8 +1293,7 @@ static inline int kvm_memslot_move_backward(struct kvm_memslots *slots,
>   	struct kvm_memory_slot *mslots = slots->memslots;
>   	int i;
>   
> -	if (WARN_ON_ONCE(slots->id_to_index[memslot->id] == -1) ||
> -	    WARN_ON_ONCE(!slots->used_slots))
> +	if (slots->id_to_index[memslot->id] == -1 || !slots->used_slots)
>   		return -1;
>   
>   	/*
> @@ -1398,6 +1397,9 @@ static void update_memslots(struct kvm_memslots *slots,
>   			i = kvm_memslot_move_backward(slots, memslot);
>   		i = kvm_memslot_move_forward(slots, memslot, i);
>   
> +		if (WARN_ON_ONCE(i < 0))
> +			return;
> +
>   		/*
>   		 * Copy the memslot to its new position in memslots and update
>   		 * its index accordingly.
> 


Note that WARN_ON_* is frowned upon, because it can result in crashes 
with panic_on_warn enabled, which is what some distributions do enable.

We tend to work around that by using pr_warn()/pr_warn_once(), avoiding 
eventually crashing the system when there is a way to continue.

-- 
Thanks,

David / dhildenb


  parent reply	other threads:[~2021-08-18 14:35 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-13 19:33 [PATCH v4 00/13] KVM: Scalable memslots implementation Maciej S. Szmigiero
2021-08-13 19:33 ` [PATCH v4 01/13] KVM: x86: Cache total page count to avoid traversing the memslot array Maciej S. Szmigiero
2021-08-13 19:33 ` [PATCH v4 02/13] KVM: x86: Don't call kvm_mmu_change_mmu_pages() if the count hasn't changed Maciej S. Szmigiero
2021-08-13 19:33 ` [PATCH v4 03/13] KVM: Add "old" memslot parameter to kvm_arch_prepare_memory_region() Maciej S. Szmigiero
2021-08-13 19:33 ` [PATCH v4 04/13] KVM: x86: Move n_memslots_pages recalc " Maciej S. Szmigiero
2021-08-13 19:33 ` [PATCH v4 05/13] KVM: Integrate gfn_to_memslot_approx() into search_memslots() Maciej S. Szmigiero
2021-08-18 14:29   ` Claudio Imbrenda
2021-08-13 19:33 ` [PATCH v4 06/13] KVM: Move WARN on invalid memslot index to update_memslots() Maciej S. Szmigiero
2021-08-18 14:29   ` Claudio Imbrenda
2021-08-18 14:35   ` David Hildenbrand [this message]
2021-08-18 21:43     ` Maciej S. Szmigiero
2021-08-20  9:27       ` David Hildenbrand
2021-08-13 19:33 ` [PATCH v4 07/13] KVM: Just resync arch fields when slots_arch_lock gets reacquired Maciej S. Szmigiero
2021-08-13 19:33 ` [PATCH v4 08/13] KVM: Resolve memslot ID via a hash table instead of via a static array Maciej S. Szmigiero
2021-08-13 19:33 ` [PATCH v4 09/13] KVM: Use interval tree to do fast hva lookup in memslots Maciej S. Szmigiero
2021-08-13 19:33 ` [PATCH v4 10/13] KVM: s390: Introduce kvm_s390_get_gfn_end() Maciej S. Szmigiero
2021-08-18 14:31   ` Claudio Imbrenda
2021-08-13 19:33 ` [PATCH v4 11/13] KVM: Keep memslots in tree-based structures instead of array-based ones Maciej S. Szmigiero
2021-08-13 19:33 ` [PATCH v4 12/13] KVM: Optimize gfn lookup in kvm_zap_gfn_range() Maciej S. Szmigiero
2021-08-13 19:33 ` [PATCH v4 13/13] KVM: Optimize overlapping memslots check Maciej S. Szmigiero

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