linux-kernel - Re: [PATCH v3 1/1] KVM: arm64: Allow cacheable stage 2 mapping using VMA flags

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Message-ID: <20250319192246.GQ9311@nvidia.com>
Date: Wed, 19 Mar 2025 16:22:46 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Oliver Upton <oliver.upton@...ux.dev>, Marc Zyngier <maz@...nel.org>,
	Ankit Agrawal <ankita@...dia.com>,
	"joey.gouly@....com" <joey.gouly@....com>,
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	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 1/1] KVM: arm64: Allow cacheable stage 2 mapping using
 VMA flags

On Wed, Mar 19, 2025 at 06:11:02PM +0000, Catalin Marinas wrote:
> On Wed, Mar 19, 2025 at 02:04:29PM -0300, Jason Gunthorpe wrote:
> > On Wed, Mar 19, 2025 at 12:01:29AM -0700, Oliver Upton wrote:
> > > You have a very good point that KVM is broken for cacheable PFNMAP'd
> > > crap since we demote to something non-cacheable, and maybe that
> > > deserves fixing first. Hopefully nobody notices that we've taken away
> > > the toys...
> > 
> > Fixing it is either faulting all access attempts or mapping it
> > cachable to the S2 (as this series is trying to do)..
> 
> As I replied earlier, it might be worth doing both - fault on !FWB
> hardware (or rather reject the memslot creation), cacheable S2
> otherwise.

I have no objection, Ankit are you able to make a failure patch?

Jason