linux-kernel - Re: [PATCH v2 0/1] KVM: arm64: Map GPU memory with no struct pages

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Message-ID: <20241210141806.GI2347147@nvidia.com>
Date: Tue, 10 Dec 2024 10:18:06 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Will Deacon <will@...nel.org>
Cc: ankita@...dia.com, maz@...nel.org, oliver.upton@...ux.dev,
	joey.gouly@....com, suzuki.poulose@....com, yuzenghui@...wei.com,
	catalin.marinas@....com, ryan.roberts@....com, shahuang@...hat.com,
	lpieralisi@...nel.org, aniketa@...dia.com, cjia@...dia.com,
	kwankhede@...dia.com, targupta@...dia.com, vsethi@...dia.com,
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	kevin.tian@...el.com, yi.l.liu@...el.com, ardb@...nel.org,
	akpm@...ux-foundation.org, gshan@...hat.com, linux-mm@...ck.org,
	kvmarm@...ts.linux.dev, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 0/1] KVM: arm64: Map GPU memory with no struct pages

On Tue, Dec 10, 2024 at 02:07:40PM +0000, Will Deacon wrote:
> On Mon, Nov 18, 2024 at 01:19:57PM +0000, ankita@...dia.com wrote:
> > The changes are heavily influenced by the insightful discussions between
> > Catalin Marinas and Jason Gunthorpe [1] on v1. Many thanks for their
> > valuable suggestions.
> > 
> > Link: https://lore.kernel.org/lkml/20230907181459.18145-2-ankita@nvidia.com [1]
> 
> That's a different series, no? It got merged at v9:

I was confused by this too. v1 of that series included this patch, as
that series went along it became focused only on enabling WC
(Normal-NC) in a VM for device MMIO and this patch for device cachable
memory was dropped off.

There are two related things:
 1) Device MMIO memory should be able to be Normal-NC in a VM. Already
    merged
 2) Device Cachable memory (ie CXL and pre-CXL coherently attached
    memory) should be Normal Cachable in a VM, even if it doesn't have
    struct page/etc. (this patch)

IIRC this part was dropped off because of the MTE complexity that
Catalin raised.

Jason