Messages in this thread | | | Date | Mon, 7 Feb 2022 08:08:15 -0600 | Subject | Re: [PATCHv2 26/29] x86/tdx: ioapic: Add shared bit for IOAPIC base address | From | Tom Lendacky <> |
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On 2/4/22 16:31, Kirill A. Shutemov wrote: > On Wed, Feb 02, 2022 at 02:33:16AM +0100, Thomas Gleixner wrote: >> On Mon, Jan 24 2022 at 18:02, Kirill A. Shutemov wrote: >>> 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? > > Hm. Good question. > > I think it is because FIXMAP_PAGE_NOCACHE does not have __ENC bit set so > the mapping is accessible to host. With TDX the logic is oposit: > everything is private if the bit is not set. > > Tom, does it sound right?
Correct, FIXMAP_PAGE_NOCACHE => PAGE_KERNEL_IO_NOCACHE, which does not have the encryption bit set, so it is mapped as shared under SEV.
Thanks, Tom
> > BTW, I will drop 'if (cc_platform_has(CC_ATTR_GUEST_TDX))'. > pgprot_decrypted() is nop on AMD in this case. >
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