linux-kernel - Re: [PATCH V4 07/11] vfio/pci: Update stale comment

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Date:   Fri, 28 Apr 2023 11:24:25 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "yishaih@...dia.com" <yishaih@...dia.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "darwi@...utronix.de" <darwi@...utronix.de>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Liu, Jing2" <jing2.liu@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "tom.zanussi@...ux.intel.com" <tom.zanussi@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V4 07/11] vfio/pci: Update stale comment

Hi Kevin,

On 4/27/2023 11:42 PM, Tian, Kevin wrote:
>> From: Chatre, Reinette <reinette.chatre@...el.com>
>> Sent: Friday, April 28, 2023 1:36 AM
>>
>> @@ -419,11 +419,9 @@ static int vfio_msi_set_vector_signal(struct
>> vfio_pci_core_device *vdev,
>>  	}
>>
>>  	/*
>> -	 * The MSIx vector table resides in device memory which may be
>> cleared
>> -	 * via backdoor resets. We don't allow direct access to the vector
>> -	 * table so even if a userspace driver attempts to save/restore
>> around
>> -	 * such a reset it would be unsuccessful. To avoid this, restore the
>> -	 * cached value of the message prior to enabling.
>> +	 * If the vector was previously allocated, refresh the on-device
>> +	 * message data before enabling in case it had been cleared or
>> +	 * corrupted since writing.
>>  	 */
>>  	cmd = vfio_pci_memory_lock_and_enable(vdev);
>>  	if (msix) {
> 
> What about keeping backdoor reset as an example, e.g.
> 
> "in case it had been cleared or corrupted (e.g. due to backdoor resets) ..."
> 
> otherwise one may doubt whether it is a more severe problem causing
> the corruption inadvertently w/o userspace driver's awareness and then
> whether just restoring the data is sufficient to move on.

Will do. Thank you very much.

Reinette