linux-kernel - RE: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified range to map as encrypted

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Message-ID: <BYAPR21MB1688F68888213E5395396DD9D7AB9@BYAPR21MB1688.namprd21.prod.outlook.com>
Date:   Thu, 23 Feb 2023 20:01:31 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Borislav Petkov <bp@...en8.de>,
        Sean Christopherson <seanjc@...gle.com>
CC:     Dave Hansen <dave.hansen@...el.com>,
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Subject: RE: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified range
 to map as encrypted

From: Borislav Petkov <bp@...en8.de> Sent: Thursday, February 23, 2023 2:45 AM
> 
> On Wed, Feb 22, 2023 at 05:21:27PM -0800, Sean Christopherson wrote:
> 
> > All I'm advocating is that for determining whether or not a device should be mapped
> > private vs. shared, provide an API so that the hypervisor-specific enlightened code
> > can manage that insanity without polluting common code.  If we are ever fortunate
> > enough to have common enumeration, e.g. through ACPI or something, the enlightened
> > code can simply reroute to the common code.  This is a well established pattern for
> > many paravirt features, I don't see why it wouldn't work here.
> 
> Yah, that would be good.

Just so I'm clear, are you saying you are good with the proposal that Sean
sketched out with code here? [1]   With his proposal, the device driver
is not involved in deciding whether to map encrypted or decrypted.  That
decision is made in the hypervisor-specific callback function based on
the physical address.   The callback has to be made in two places in common
code.  But then as Sean said, " the hypervisor-specific enlightened code
can manage that insanity without polluting common code". :-)

I like Sean's proposal, so if you are good with it, I'll do v6 of the patch
set with that approach.

Dave Hansen:  Are you also OK with Sean's proposal?  Looking for consensus
here ....

> If the device can know upfront how it needs to
> ioremap its address range, then that is fine - we already have
> ioremap_encrypted() for example.
> 

Again, the device driver would not be involved in Sean's proposal.

Michael

[1] https://lore.kernel.org/linux-hyperv/Y+bXjxUtSf71E5SS@google.com/