From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH v5 16/16] x86/tdx: Add cmdline option to force use of
 ioremap_host_shared
Date: Thu, 14 Oct 2021 22:50:59 -0700
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Cc: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Peter Zijlstra <peterz@infradead.org>, Andy Lutomirski <luto@kernel.org>, Bjorn Helgaas <bhelgaas@google.com>, Richard Henderson <rth@twiddle.net>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>, James E J Bottomley <James.Bottomley@hansenpartnership.com>, Helge Deller <deller@gmx.de>, "David S . Miller" <davem@davemloft.net>, Arnd Bergmann <arnd@arndb.de>, Jonathan Corbet <corbet@lwn.net>, Paolo Bonzini <pbonzini@redhat.com>, David Hildenbrand <david@redhat.com>, Andrea Arcangeli <aarcange@redhat.com>, Josh Poimboeuf <jpoimboe@redhat.com>, Peter H Anvin <hpa@zytor.com>


> I thought you basically create an OperationRegion of SystemMemory type,
> and off you go. Maybe the OSPM in Linux is clever and protects
> some memory, I wouldn't know.


I investigated this now, and it looks like acpi is using 
ioremap_cache(). We can hook into that and force non sharing. It's 
probably safe to assume that this is not used on real IO devices.

I think there are still some other BIOS mappings that use just plain 
ioremap() though.


-Andi