Commit 65fab5bc authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Dave Hansen
Browse files

x86/tdx: Exclude shared bit from __PHYSICAL_MASK 



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: default avatarKuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: default avatarKuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarAndi Kleen <ak@linux.intel.com>
Reviewed-by: default avatarTony Luck <tony.luck@intel.com>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20220405232939.73860-6-kirill.shutemov@linux.intel.com
parent 41394e33

arch/x86/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -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.

arch/x86/coco/tdx/tdx.c

+8 −0
Original line number Diff line number Diff line
@@ -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");

}