linux-kernel - Re: [PATCH v1 1/2] KVM: arm64: determine memory type from VMA

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Message-ID: <20240319133844.GA159172@nvidia.com>
Date: Tue, 19 Mar 2024 10:38:44 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Ankit Agrawal <ankita@...dia.com>
Cc: Catalin Marinas <catalin.marinas@....com>,
	"maz@...nel.org" <maz@...nel.org>,
	"oliver.upton@...ux.dev" <oliver.upton@...ux.dev>,
	"will@...nel.org" <will@...nel.org>,
	Aniket Agashe <aniketa@...dia.com>, Neo Jia <cjia@...dia.com>,
	Kirti Wankhede <kwankhede@...dia.com>,
	"Tarun Gupta (SW-GPU)" <targupta@...dia.com>,
	Vikram Sethi <vsethi@...dia.com>, Andy Currid <acurrid@...dia.com>,
	Alistair Popple <apopple@...dia.com>,
	John Hubbard <jhubbard@...dia.com>, Dan Williams <danw@...dia.com>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"kvmarm@...ts.linux.dev" <kvmarm@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/2] KVM: arm64: determine memory type from VMA

On Sun, Mar 10, 2024 at 03:49:36AM +0000, Ankit Agrawal wrote:
> Bringing this to the fore.
> 
> >> Where does that leave us for this patch? We check the VM_MTE_ALLOWED
> >> and check for ZONE_MOVABLE struct pages as one of the conditions for
> >> NORMAL?
> >
> > I think we should keep it as simple as possible and, looking at it
> > again, maybe even ignore vm_page_prot. Two questions though:
> >
> > 1. Does VM_IO imply vm_page_prot never having MT_NORMAL or
> >    MT_NORMAL_TAGGED?

Drivers do crazy things, so I would not be surprised if something in
the tree does this (wrong) thing. We can check the pgprot in the vma
as well as the VM_IO to make the decision.

> > 2. Do all I/O ranges (side-effects, non-RAM) mapped into a guest (and
> >   which end up in user_mem_abort()) imply VM_IO?

Yes, this is definately true for VFIO.

Jason