linux-kernel - RE: [PATCHv2 26/29] x86/tdx: ioapic: Add shared bit for IOAPIC base address

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Message-ID: <BYAPR11MB26472C6C7699265971A5EDAE8C299@BYAPR11MB2647.namprd11.prod.outlook.com>
Date:   Fri, 4 Feb 2022 22:09:58 +0000
From:   "Yamahata, Isaku" <isaku.yamahata@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>
CC:     "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "aarcange@...hat.com" <aarcange@...hat.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "Gross, Jurgen" <jgross@...e.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "Poimboe, Josh" <jpoimboe@...hat.com>,
        "knsathya@...nel.org" <knsathya@...nel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "sdeep@...are.com" <sdeep@...are.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "wanpengli@...cent.com" <wanpengli@...cent.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: RE: [PATCHv2 26/29] x86/tdx: ioapic: Add shared bit for IOAPIC base
 address

> > ioremap()-created mappings such as virtio will be marked as
> > shared. However, the IOAPIC code does not use ioremap() and instead
> > uses the fixmap mechanism.
> >
> > Introduce a special fixmap helper just for the IOAPIC code.  Ensure
> > that it marks IOAPIC pages as "shared".  This replaces
> > set_fixmap_nocache() with __set_fixmap() since __set_fixmap()
> > allows custom 'prot' values.
> 
> Why is this a TDX only issue and SEV does not suffer from that?

The bit meaning is opposite. 
TDX: set: shared, cleared: private
SEV: set: private, cleared: shared

Without this patch, it happens to work for SEV. (or any emulated MMIO can work)
But for TDX, IOAPIC emulation doesn't work.

Thanks,
Isaku Yamahata