linux-kernel - Re: [PATCH v5 08/14] iommufd/viommu: Add iommufd_viommu_report

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Message-ID: <Z5CbGKYbwy+qPjyh@nvidia.com>
Date: Tue, 21 Jan 2025 23:15:36 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: <kevin.tian@...el.com>, <corbet@....net>, <will@...nel.org>,
	<joro@...tes.org>, <suravee.suthikulpanit@....com>, <robin.murphy@....com>,
	<dwmw2@...radead.org>, <baolu.lu@...ux.intel.com>, <shuah@...nel.org>,
	<linux-kernel@...r.kernel.org>, <iommu@...ts.linux.dev>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kselftest@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <eric.auger@...hat.com>,
	<jean-philippe@...aro.org>, <mdf@...nel.org>, <mshavit@...gle.com>,
	<shameerali.kolothum.thodi@...wei.com>, <smostafa@...gle.com>,
	<ddutile@...hat.com>, <yi.l.liu@...el.com>, <patches@...ts.linux.dev>
Subject: Re: [PATCH v5 08/14] iommufd/viommu: Add iommufd_viommu_report_event
 helper

On Tue, Jan 21, 2025 at 08:21:28PM -0400, Jason Gunthorpe wrote:
> On Tue, Jan 21, 2025 at 01:40:05PM -0800, Nicolin Chen wrote:
> > > There is also the minor detail of what happens if the hypervisor HW
> > > queue overflows - I don't know the answer here. It is security
> > > concerning since the VM can spam DMA errors at high rate. :|
> > 
> > In my view, the hypervisor queue is the vHW queue for the VM, so
> > it should act like a HW, which means it's up to the guest kernel
> > driver that handles the high rate DMA errors..
> 
> I'm mainly wondering what happens if the single physical kernel
> event queue overflows because it is DOS'd by a VM and the hypervisor
> cannot drain it fast enough?
> 
> I haven't looked closely but is there some kind of rate limiting or
> otherwise to mitigate DOS attacks on the shared event queue from VMs?

SMMUv3 reads the event out of the physical kernel event queue,
and adds that to faultq or veventq or prints it out. So, it'd
not overflow because of DOS? And all other drivers should do
the same?

Thanks
Nicolin