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ac3a220884
The TDX module uses additional metadata to record things like which
guest "owns" a given page of memory. This metadata, referred as
Physical Address Metadata Table (PAMT), essentially serves as the
'struct page' for the TDX module. PAMTs are not reserved by hardware
up front. They must be allocated by the kernel and then given to the
TDX module during module initialization.
TDX supports 3 page sizes: 4K, 2M, and 1G. Each "TD Memory Region"
(TDMR) has 3 PAMTs to track the 3 supported page sizes. Each PAMT must
be a physically contiguous area from a Convertible Memory Region (CMR).
However, the PAMTs which track pages in one TDMR do not need to reside
within that TDMR but can be anywhere in CMRs. If one PAMT overlaps with
any TDMR, the overlapping part must be reported as a reserved area in
that particular TDMR.
Use alloc_contig_pages() since PAMT must be a physically contiguous area
and it may be potentially large (~1/256th of the size of the given TDMR).
The downside is alloc_contig_pages() may fail at runtime. One (bad)
mitigation is to launch a TDX guest early during system boot to get
those PAMTs allocated at early time, but the only way to fix is to add a
boot option to allocate or reserve PAMTs during kernel boot.
It is imperfect but will be improved on later.
TDX only supports a limited number of reserved areas per TDMR to cover
both PAMTs and memory holes within the given TDMR. If many PAMTs are
allocated within a single TDMR, the reserved areas may not be sufficient
to cover all of them.
Adopt the following policies when allocating PAMTs for a given TDMR:
- Allocate three PAMTs of the TDMR in one contiguous chunk to minimize
the total number of reserved areas consumed for PAMTs.
- Try to first allocate PAMT from the local node of the TDMR for better
NUMA locality.
Also dump out how many pages are allocated for PAMTs when the TDX module
is initialized successfully. This helps answer the eternal "where did
all my memory go?" questions.
[ dhansen: merge in error handling cleanup ]
Signed-off-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Isaku Yamahata <isaku.yamahata@intel.com>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Yuan Yao <yuan.yao@intel.com>
Link: https://lore.kernel.org/all/20231208170740.53979-11-dave.hansen%40intel.com
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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.