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

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Message-ID: <20250122002128.GC5556@nvidia.com>
Date: Tue, 21 Jan 2025 20:21:28 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...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 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?

Jason