linux-kernel - Re: [Patch v2] KVM: x86: Initializing all kvm_lapic_irq fields in ioapic_write

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Message-ID: <4acfacb2-9509-0f1d-24d8-dbbda1944088@redhat.com>
Date:   Sat, 14 Mar 2020 10:45:57 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Nitesh Narayan Lal <nitesh@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        mtosatti@...hat.com, sean.j.christopherson@...el.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        peterx@...hat.com
Subject: Re: [Patch v2] KVM: x86: Initializing all kvm_lapic_irq fields in
 ioapic_write_indirect

On 13/03/20 17:38, Nitesh Narayan Lal wrote:
> 
> On 3/13/20 12:36 PM, Vitaly Kuznetsov wrote:
>> Nitesh Narayan Lal <nitesh@...hat.com> writes:
>>
>>> On 3/13/20 12:18 PM, Vitaly Kuznetsov wrote:
>>>> Nitesh Narayan Lal <nitesh@...hat.com> writes:
>>>>
>>>>> On 3/13/20 9:38 AM, Nitesh Narayan Lal wrote:
>>>>>> On 3/13/20 9:25 AM, Vitaly Kuznetsov wrote:
>>>>>>> Nitesh Narayan Lal <nitesh@...hat.com> writes:
>>>>>>>
>>>>>>>> Previously all fields of structure kvm_lapic_irq were not initialized
>>>>>>>> before it was passed to kvm_bitmap_or_dest_vcpus(). Which will cause
>>>>>>>> an issue when any of those fields are used for processing a request.
>>>>>>>> For example not initializing the msi_redir_hint field before passing
>>>>>>>> to the kvm_bitmap_or_dest_vcpus(), may lead to a misbehavior of
>>>>>>>> kvm_apic_map_get_dest_lapic(). This will specifically happen when the
>>>>>>>> kvm_lowest_prio_delivery() returns TRUE due to a non-zero garbage
>>>>>>>> value of msi_redir_hint, which should not happen as the request belongs
>>>>>>>> to APIC fixed delivery mode and we do not want to deliver the
>>>>>>>> interrupt only to the lowest priority candidate.
>>>>>>>>
>>>>>>>> This patch initializes all the fields of kvm_lapic_irq based on the
>>>>>>>> values of ioapic redirect_entry object before passing it on to
>>>>>>>> kvm_bitmap_or_dest_vcpus().
>>>>>>>>
>>>>>>>> Fixes: 7ee30bc132c6("KVM: x86: deliver KVM IOAPIC scan request to target vCPUs")
>>>>>>>> Signed-off-by: Nitesh Narayan Lal <nitesh@...hat.com>
>>>>>>>> ---
>>>>>>>>  arch/x86/kvm/ioapic.c | 7 +++++--
>>>>>>>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
>>>>>>>> index 7668fed..3a8467d 100644
>>>>>>>> --- a/arch/x86/kvm/ioapic.c
>>>>>>>> +++ b/arch/x86/kvm/ioapic.c
>>>>>>>> @@ -378,12 +378,15 @@ static void ioapic_write_indirect(struct kvm_ioapic *ioapic, u32 val)
>>>>>>>>  		if (e->fields.delivery_mode == APIC_DM_FIXED) {
>>>>>>>>  			struct kvm_lapic_irq irq;
>>>>>>>>  
>>>>>>>> -			irq.shorthand = APIC_DEST_NOSHORT;
>>>>>>>>  			irq.vector = e->fields.vector;
>>>>>>>>  			irq.delivery_mode = e->fields.delivery_mode << 8;
>>>>>>>> -			irq.dest_id = e->fields.dest_id;
>>>>>>>>  			irq.dest_mode =
>>>>>>>>  			    kvm_lapic_irq_dest_mode(!!e->fields.dest_mode);
>>>>>>>> +			irq.level = 1;
>>>>>>> 'level' is bool in struct kvm_lapic_irq but other than that, is there a
>>>>>>> reason we set it to 'true' here? I understand that any particular
>>>>>>> setting is likely better than random
>>>>>> Yes, that is the only reason which I had in my mind while doing this change.
>>>>>> I was not particularly sure about the value, so I copied what ioapic_serivce()
>>>>>> is doing.
>>>>> Do you think I should skip setting this here?
>>>>>
>>>> Personally, i'd initialize it to 'false': usualy, if something is not
>>>> properly initialized it's either 0 or garbage)
>>> I think that's true, initializing it to 'false' might make more sense.
>>> Any other concerns or comments that I can improve?
>>>
>> Please add the missing space to the 'Fixes' tag:
>>
>> Fixes: 7ee30bc132c6 ("KVM: x86: deliver KVM IOAPIC scan request to target vCPUs")
> 
> My bad.
> 
>>
>> and with that and irq.level initialized to 'false' feel free to add
>>
>> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>>
>> tag. Thanks!
> 
> Sure, thank you.

I did the changes and applied the patch, thanks.

Paolo




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