linux-kernel - Re: [PATCH v6 14/14] iommu/arm-smmu-v3: Set MEV bit in nested STE for DoS mitigations

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Message-ID: <Z7bV8q8h5ssgiucv@Asurada-Nvidia>
Date: Wed, 19 Feb 2025 23:12:50 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Pranjal Shrivastava <praan@...gle.com>, "Tian, Kevin"
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Subject: Re: [PATCH v6 14/14] iommu/arm-smmu-v3: Set MEV bit in nested STE
 for DoS mitigations

On Tue, Feb 18, 2025 at 02:52:29PM -0400, Jason Gunthorpe wrote:
> On Tue, Feb 18, 2025 at 06:17:15PM +0000, Pranjal Shrivastava wrote:
> 
> > > Is MEV available only in nested mode? Otherwise it perhaps makes
> > > sense to turn it on in all configurations in IOMMUFD paths...
> > 
> > I think the arm-smmu-v3's iommufd implementation only supports nested
> > which could be the reason.
> 
> I think starting with MEV in this limited case is reasonable.
> 
> I agree it makes sense to always turn it on from a production
> perspective..

Then, I will just add a line to the commit log:
"In the future, we might want to enable the MEV for non-nested cases too
 such as domain->type == IOMMU_DOMAIN_UNMANAGED or even IOMMU_DOMAIN_DMA."

Thanks
Nicolin