linux-kernel - Re: [PATCH 4/5] vfio/type1: Flush CPU caches on DMA pages in non-coherent domains

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Date: Wed, 22 May 2024 13:52:21 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: "Tian, Kevin" <kevin.tian@...el.com>,
	"Vetter, Daniel" <daniel.vetter@...el.com>,
	"Zhao, Yan Y" <yan.y.zhao@...el.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"seanjc@...gle.com" <seanjc@...gle.com>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
	"luto@...nel.org" <luto@...nel.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
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	"robin.murphy@....com" <robin.murphy@....com>,
	"baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
	"Liu, Yi L" <yi.l.liu@...el.com>
Subject: Re: [PATCH 4/5] vfio/type1: Flush CPU caches on DMA pages in
 non-coherent domains

On Wed, May 22, 2024 at 08:43:18AM -0600, Alex Williamson wrote:

> But I think this also means that regardless of virtualizing
> PCI_EXP_DEVCTL_NOSNOOP_EN, there will be momentary gaps around device
> resets where a device could legitimately perform no-snoop
> transactions.

Isn't memory enable turned off after FLR? If not do we have to make it
off before doing FLR?

I'm not sure how a no-snoop could leak out around FLR?

Jason