linux-kernel - Re: Re: [PATCH v17 19/35] arch/mm: Export direct {un,}map functions

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Date: Mon, 26 Feb 2024 09:27:31 -0800
From: Elliot Berman <quic_eberman@...cinc.com>
To: David Hildenbrand <david@...hat.com>
CC: Christoph Hellwig <hch@...radead.org>, Will Deacon <will@...nel.org>,
        Quentin Perret <qperret@...gle.com>,
        Chris Goldsworthy
	<quic_cgoldswo@...cinc.com>,
        Android KVM <android-kvm@...gle.com>,
        "Patrick
 Daly" <quic_pdaly@...cinc.com>,
        Alex Elder <elder@...aro.org>,
        "Srinivas
 Kandagatla" <srinivas.kandagatla@...aro.org>,
        Murali Nalajal
	<quic_mnalajal@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        "Srivatsa
 Vaddagiri" <quic_svaddagi@...cinc.com>,
        Carl van Schaik
	<quic_cvanscha@...cinc.com>,
        Philip Derrin <quic_pderrin@...cinc.com>,
        Prakruthi Deepak Heragu <quic_pheragu@...cinc.com>,
        Jonathan Corbet
	<corbet@....net>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski
	<krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Konrad Dybcio
	<konrad.dybcio@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>,
        "Dmitry
 Baryshkov" <dmitry.baryshkov@...aro.org>,
        Fuad Tabba <tabba@...gle.com>,
        "Sean Christopherson" <seanjc@...gle.com>,
        Andrew Morton
	<akpm@...ux-foundation.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-mm@...ck.org>
Subject: Re: Re: [PATCH v17 19/35] arch/mm: Export direct {un,}map functions

On Mon, Feb 26, 2024 at 12:53:48PM +0100, David Hildenbrand wrote:
> On 26.02.24 12:06, Christoph Hellwig wrote:
> > The point is that we can't we just allow modules to unmap data from
> > the kernel mapping, no matter how noble your intentions are.
> 
> I absolutely agree.
> 

Hi David and Chirstoph,

Are your preferences that we should make Gunyah builtin only or should add
fixing up S2 PTW errors (or something else)?

Also, do you extend that preference to modifying S2 mappings? This would
require any hypervisor driver that supports confidential compute
usecases to only ever be builtin.

Is your concern about unmapping data from kernel mapping, then module
being unloaded, and then having no way to recover the mapping? Would a
permanent module be better? The primary reason we were wanting to have
it as module was to avoid having driver in memory if you're not a Gunyah
guest.

Thanks,
Elliot