linux-kernel - Re: [PATCH v3 00/21] TDX host kernel support

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Message-ID: <915ed339-f5e6-c31f-ffe1-a80402ce78dd@intel.com>
Date:   Fri, 29 Apr 2022 14:27:16 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Kai Huang <kai.huang@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        KVM list <kvm@...r.kernel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Brown, Len" <len.brown@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        Rafael J Wysocki <rafael.j.wysocki@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andi Kleen <ak@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Isaku Yamahata <isaku.yamahata@...el.com>
Subject: Re: [PATCH v3 00/21] TDX host kernel support

On 4/29/22 14:20, Dan Williams wrote:
> Is there something already like this today for people that, for
> example, attempt to use PCI BAR mappings as memory? Or does KVM simply
> allow for garbage-in garbage-out?

I'm just guessing, but I _assume_ those garbage PCI BAR mappings are how
KVM does device passthrough.

I know that some KVM users even use mem= to chop down the kernel-owned
'struct page'-backed memory, then have a kind of /dev/mem driver to let
the memory get mapped back into userspace.  KVM is happy to pass through
those mappings.