From: Chao Gao <chao.gao@intel.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] Reset pass-thru devices in a VM
Date: Fri, 9 Aug 2019 22:13:37 +0800 [thread overview]
Message-ID: <20190809141336.GA17062@gao-cwp> (raw)
In-Reply-To: <b3887a04-a7a0-61ee-2037-36322c388d6b@suse.com>
On Fri, Aug 09, 2019 at 03:23:59PM +0200, Jan Beulich wrote:
>On 09.08.2019 15:24, Chao Gao wrote:
>>On Fri, Aug 09, 2019 at 10:49:32AM +0200, Jan Beulich wrote:
>>>On 09.08.2019 10:38, Chao Gao wrote:
>>>>Alternatively, emulating FLR (Function Level Reset)
>>>>capability for this device might be a feasible way and only needs
>>>>relatively few changes. I am planning to enable an opt-in feature
>>>>(like 'permissive') to allow qemu to expose FLR capability to guest for
>>>>pass-thru devices as long as this device is resetable on dom0 (i.e. the
>>>>device has 'reset' attribute under its sysfs). And when guest initiates
>>>>an FLR, qemu just echo 1 to the 'reset' attribute on dom0.
>>>>
>>>>Do you think emulating FLR capability is doable?
>>>
>>>Wouldn't a such emulated guest initiated reset affect other devices
>>>(likely not under control of this guest) as well?
>>
>>No. Linux kernel guarantees that reset to a device won't affect
>>other devices. Otherwise, such device cannot be reset and no
>>'reset' attribute will be created under device's sysfs.
>>Specfically, the invocation of pci_dev_reset_slot_function() and
>>pci_parent_bus_reset() in pci_probe_reset_function() will check whether
>>the device (function) is the only one under the slot or bus
>>respectively. In pci_create_capabilities_sysfs(), 'reset' attribute is
>>created only if dev->reset_fn is not zero.
>
>Ah, good. But then the opposite question arises: How would your
>proposed change help if the device shares a bus with others?
It wouldn't. If the device supports any way to reset it in dom0, this
change would help. If even in dom0 there is no way to reset a device,
it won't help. But I think for such device, it cannot be safely assigned
to a VM because we rely on PCI reset to clean up sensitive data in the
device programmed by the previous owner.
Thanks
Chao
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next prev parent reply other threads:[~2019-08-09 14:10 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-09 8:38 [Xen-devel] Reset pass-thru devices in a VM Chao Gao
2019-08-09 8:49 ` Jan Beulich
2019-08-09 13:24 ` Chao Gao
2019-08-09 13:23 ` Jan Beulich
2019-08-09 14:13 ` Chao Gao [this message]
2019-08-09 12:42 ` Roger Pau Monné
2019-08-09 13:57 ` Chao Gao
2019-08-26 21:17 ` Pasi Kärkkäinen
2019-08-27 4:40 ` Chao Gao
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