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

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Message-ID: <20250123134342.GP5556@nvidia.com>
Date: Thu, 23 Jan 2025 09:43:42 -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 Wed, Jan 22, 2025 at 11:02:59PM -0800, Nicolin Chen wrote:

> I made a change to duplicate the overflow node in the fetch() that
> is protected by the spinlock, which is used for copy_to_user. Then
> the other routine for vEVENT reporting, protected by the spinlock,
> can race-freely update the preallocated overflow node.

That seems like the right answer, copy the few bytes you need on
the stack under the spinlock.

Jason