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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
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.