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Subject: RE: [PATCHv2 26/29] x86/tdx: ioapic: Add shared bit for IOAPIC base
 address
Thread-Topic: [PATCHv2 26/29] x86/tdx: ioapic: Add shared bit for IOAPIC base
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Thread-Index: AQHYETNpIDxA5Tu5KEmB7cgjSERHHqx/h0wAgAR4eQA=
Date:   Fri, 4 Feb 2022 22:09:58 +0000
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References: <20220124150215.36893-1-kirill.shutemov@linux.intel.com>
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 <871r0mvyqr.ffs@tglx>
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> > 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.
>=20
> Why is this a TDX only issue and SEV does not suffer from that?

The bit meaning is opposite.=20
TDX: set: shared, cleared: private
SEV: set: private, cleared: shared

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

Thanks,
Isaku Yamahata