linux-kernel - Re: [PATCH v5 16/16] x86/tdx: Add cmdline option to force use of ioremap_host

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Message-ID: <20211011142330-mutt-send-email-mst@kernel.org>
Date:   Mon, 11 Oct 2021 14:28:51 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Richard Henderson <rth@...ddle.net>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        James E J Bottomley <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
        "David S . Miller" <davem@...emloft.net>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-alpha@...r.kernel.org,
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        sparclinux@...r.kernel.org, linux-arch@...r.kernel.org,
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        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v5 16/16] x86/tdx: Add cmdline option to force use of
 ioremap_host_shared

On Mon, Oct 11, 2021 at 10:35:18AM -0700, Andi Kleen wrote:
> 
> > Presumably bios code is in arch/x86 and drivers/acpi, right?
> > Up to 200 calls the majority of which is likely private ...
> 
> Yes.
> 
> > I don't have better ideas but the current setup will just
> > result in people making their guests vulnerable whenever they
> > want to allow device pass-through.
> 
> 
> Yes that's true. For current TDX our target is virtual devices only. But if
> pass through usage will be really wide spread we may need to revisit.
> 
> 
> -Andi

I mean ... it's already wide spread. If we support it with TDX
it will be used with TDX. If we don't then I guess it won't,
exposing this kind of limitation in a userspace visible way isn't great
though. I guess it boils down to the fact that
ioremap_host_shared is just not a great interface, users simply
have no idea whether a given driver uses ioremap.

-- 
MST