From: David Hildenbrand <david@redhat.com>
To: "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>
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,
Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH v4 06/13] KVM: Move WARN on invalid memslot index to update_memslots()
Date: Fri, 20 Aug 2021 11:27:42 +0200 [thread overview]
Message-ID: <633bf50b-5de4-1e76-736c-067d10bf92b3@redhat.com> (raw)
In-Reply-To: <fa71d652-8b7f-e0d7-5617-8958e3e78f6e@maciej.szmigiero.name>
On 18.08.21 23:43, Maciej S. Szmigiero wrote:
> On 18.08.2021 16:35, David Hildenbrand wrote:
>> 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.
>>
>
> This patch uses WARN_ON_ONCE because:
> 1) It was used in the old code and the patch merely moves the check
> from kvm_memslot_move_backward() to its caller,
>
> 2) This chunk of code is wholly replaced by patch 11 from this series
> anyway ("Keep memslots in tree-based structures instead of array-based ones").
Okay, that makes sense then, thanks!
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-08-20 9:27 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
2021-08-18 21:43 ` Maciej S. Szmigiero
2021-08-20 9:27 ` David Hildenbrand [this message]
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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