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x86/tdx: Exclude shared bit from __PHYSICAL_MASK

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In TDX guests, by default memory is protected from host access. If a
guest needs to communicate with the VMM (like the I/O use case), it uses
a single bit in the physical address to communicate the protected/shared
attribute of the given page.

In the x86 ARCH code, __PHYSICAL_MASK macro represents the width of the
physical address in the given architecture. It is used in creating
physical PAGE_MASK for address bits in the kernel. Since in TDX guest,
a single bit is used as metadata, it needs to be excluded from valid
physical address bits to avoid using incorrect addresses bits in the
kernel.

Enable DYNAMIC_PHYSICAL_MASK to support updating the __PHYSICAL_MASK.

Co-developed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20220405232939.73860-6-kirill.shutemov@linux.intel.com
This commit is contained in:
Kirill A. Shutemov 2022-04-06 02:29:14 +03:00 committed by Dave Hansen
parent 41394e33f3
commit 65fab5bc03
2 changed files with 9 additions and 0 deletions
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1
arch/x86/Kconfig
View File

@ -883,6 +883,7 @@ config INTEL_TDX_GUEST
depends on X86_64 && CPU_SUP_INTEL
depends on X86_X2APIC
select ARCH_HAS_CC_PLATFORM
select DYNAMIC_PHYSICAL_MASK
help
Support running as a guest under Intel TDX. Without this support,
the guest kernel can not boot or run under TDX.

8
arch/x86/coco/tdx/tdx.c
View File

@ -89,5 +89,13 @@ void __init tdx_early_init(void)
cc_mask = get_cc_mask();
cc_set_mask(cc_mask);
/*
* All bits above GPA width are reserved and kernel treats shared bit
* as flag, not as part of physical address.
*
* Adjust physical mask to only cover valid GPA bits.
*/
physical_mask &= cc_mask - 1;
pr_info("Guest detected\n");
}