[PATCH v15 10/23] x86/virt/tdx: Add placeholder to construct TDMRs to cover all TDX memory regions

Kai Huang
2023-11-09T11:57:21Z

After the kernel selects all TDX-usable memory regions, the kernel needs
to pass those regions to the TDX module via data structure "TD Memory
Region" (TDMR).

Add a placeholder to construct a list of TDMRs (in multiple steps) to
cover all TDX-usable memory regions.

=== Long Version ===

TDX provides increased levels of memory confidentiality and integrity.
This requires special hardware support for features like memory
encryption and storage of memory integrity checksums. Not all memory
satisfies these requirements.

As a result, TDX introduced the concept of a "Convertible Memory Region"
(CMR). During boot, the firmware builds a list of all of the memory
ranges which can provide the TDX security guarantees. The list of these
ranges is available to the kernel by querying the TDX module.

The TDX architecture needs additional metadata to record things like
which TD guest "owns" a given page of memory. This metadata essentially
serves as the 'struct page' for the TDX module. The space for this
metadata is not reserved by the hardware up front and must be allocated
by the kernel and given to the TDX module.

Since this metadata consumes space, the VMM can choose whether or not to
allocate it for a given area of convertible memory. If it chooses not
to, the memory cannot receive TDX protections and can not be used by TDX
guests as private memory.

For every memory region that the VMM wants to use as TDX memory, it sets
up a "TD Memory Region" (TDMR). Each TDMR represents a physically
contiguous convertible range and must also have its own physically
contiguous metadata table, referred to as a Physical Address Metadata
Table (PAMT), to track status for each page in the TDMR range.

Unlike a CMR, each TDMR requires 1G granularity and alignment. To
support physical RAM areas that don't meet those strict requirements,
each TDMR permits a number of internal "reserved areas" which can be
placed over memory holes. If PAMT metadata is placed within a TDMR it
must be covered by one of these reserved areas.

Let's summarize the concepts:

CMR - Firmware-enumerated physical ranges that support TDX. CMRs are
4K aligned.
TDMR - Physical address range which is chosen by the kernel to support
TDX. 1G granularity and alignment required. Each TDMR has
reserved areas where TDX memory holes and overlapping PAMTs can
be represented.
PAMT - Physically contiguous TDX metadata. One table for each page size
per TDMR. Roughly 1/256th of TDMR in size. 256G TDMR = ~1G
PAMT.

As one step of initializing the TDX module, the kernel configures
TDX-usable memory regions by passing a list of TDMRs to the TDX module.

Constructing the list of TDMRs consists below steps:

1) Fill out TDMRs to cover all memory regions that the TDX module will
use for TD memory.
2) Allocate and set up PAMT for each TDMR.
3) Designate reserved areas for each TDMR.

Add a placeholder to construct TDMRs to do the above steps. To keep
things simple, just allocate enough space to hold maximum number of
TDMRs up front. Always free the buffer of TDMRs since they are only
used during module initialization.

Signed-off-by: Kai Huang <kai.huang@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>
---

v14 -> v15:
- Rebase due to the new TDH.SYS.RD patch (minor)
- 'struct tdsysinfo_struct' -> 'struct tdx_tdmr_sysinfo'.

v13 -> v14:
- No change.

v12 -> v13:
- No change.

v11 -> v12:
- Added tags from Dave/Kirill.

v10 -> v11:
- Changed to keep TDMRs after module initialization to deal with TDX
erratum in future patches.

v9 -> v10:
- Changed the TDMR list from static variable back to local variable as
now TDX module isn't disabled when tdx_cpu_enable() fails.

v8 -> v9:
- Changes around 'struct tdmr_info_list' (Dave):
- Moved the declaration from tdx.c to tdx.h.
- Renamed 'first_tdmr' to 'tdmrs'.
- 'nr_tdmrs' -> 'nr_consumed_tdmrs'.
- Changed 'tdmrs' to 'void *'.
- Improved comments for all structure members.
- Added a missing empty line in alloc_tdmr_list() (Dave).

v7 -> v8:
- Improved changelog to tell this is one step of "TODO list" in
init_tdx_module().
- Other changelog improvement suggested by Dave (with "Create TDMRs" to
"Fill out TDMRs" to align with the code).
- Added a "TODO list" comment to lay out the steps to construct TDMRs,
following the same idea of "TODO list" in tdx_module_init().
- Introduced 'struct tdmr_info_list' (Dave)
- Further added additional members (tdmr_sz/max_tdmrs/nr_tdmrs) to
simplify getting TDMR by given index, and reduce passing arguments
around functions.
- Added alloc_tdmr_list()/free_tdmr_list() accordingly, which internally
uses tdmr_size_single() (Dave).
- tdmr_num -> nr_tdmrs (Dave).

v6 -> v7:
- Improved commit message to explain 'int' overflow cannot happen
in cal_tdmr_size() and alloc_tdmr_array(). -- Andy/Dave.

...

---
arch/x86/virt/vmx/tdx/tdx.c | 94 ++++++++++++++++++++++++++++++++++++-
arch/x86/virt/vmx/tdx/tdx.h | 33 +++++++++++++
2 files changed, 125 insertions(+), 2 deletions(-)

diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index d24027993983..99f3b3958681 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -22,6 +22,7 @@
#include <linux/minmax.h>
#include <linux/sizes.h>
#include <linux/pfn.h>
+#include <linux/align.h>
#include <asm/msr-index.h>
#include <asm/msr.h>
#include <asm/tdx.h>
@@ -301,9 +302,84 @@ static int get_tdx_tdmr_sysinfo(struct tdx_tdmr_sysinfo *tdmr_sysinfo)
&tdmr_sysinfo->pamt_entry_size[TDX_PS_1G]);
}

+/* Calculate the actual TDMR size */
+static int tdmr_size_single(u16 max_reserved_per_tdmr)
+{
+ int tdmr_sz;
+
+ /*
+ * The actual size of TDMR depends on the maximum
+ * number of reserved areas.
+ */
+ tdmr_sz = sizeof(struct tdmr_info);
+ tdmr_sz += sizeof(struct tdmr_reserved_area) * max_reserved_per_tdmr;
+
+ return ALIGN(tdmr_sz, TDMR_INFO_ALIGNMENT);
+}
+
+static int alloc_tdmr_list(struct tdmr_info_list *tdmr_list,
+ struct tdx_tdmr_sysinfo *tdmr_sysinfo)
+{
+ size_t tdmr_sz, tdmr_array_sz;
+ void *tdmr_array;
+
+ tdmr_sz = tdmr_size_single(tdmr_sysinfo->max_reserved_per_tdmr);
+ tdmr_array_sz = tdmr_sz * tdmr_sysinfo->max_tdmrs;
+
+ /*
+ * To keep things simple, allocate all TDMRs together.
+ * The buffer needs to be physically contiguous to make
+ * sure each TDMR is physically contiguous.
+ */
+ tdmr_array = alloc_pages_exact(tdmr_array_sz,
+ GFP_KERNEL | __GFP_ZERO);
+ if (!tdmr_array)
+ return -ENOMEM;
+
+ tdmr_list->tdmrs = tdmr_array;
+
+ /*
+ * Keep the size of TDMR to find the target TDMR
+ * at a given index in the TDMR list.
+ */
+ tdmr_list->tdmr_sz = tdmr_sz;
+ tdmr_list->max_tdmrs = tdmr_sysinfo->max_tdmrs;
+ tdmr_list->nr_consumed_tdmrs = 0;
+
+ return 0;
+}
+
+static void free_tdmr_list(struct tdmr_info_list *tdmr_list)
+{
+ free_pages_exact(tdmr_list->tdmrs,
+ tdmr_list->max_tdmrs * tdmr_list->tdmr_sz);
+}
+
+/*
+ * Construct a list of TDMRs on the preallocated space in @tdmr_list
+ * to cover all TDX memory regions in @tmb_list based on the TDX module
+ * TDMR global information in @tdmr_sysinfo.
+ */
+static int construct_tdmrs(struct list_head *tmb_list,
+ struct tdmr_info_list *tdmr_list,
+ struct tdx_tdmr_sysinfo *tdmr_sysinfo)
+{
+ /*
+ * TODO:
+ *
+ * - Fill out TDMRs to cover all TDX memory regions.
+ * - Allocate and set up PAMTs for each TDMR.
+ * - Designate reserved areas for each TDMR.
+ *
+ * Return -EINVAL until constructing TDMRs is done
+ */
+ return -EINVAL;
+}
+
static int init_tdx_module(void)
{
struct tdx_tdmr_sysinfo tdmr_sysinfo;
+ struct tdmr_info_list tdmr_list;
int ret;

/*
@@ -326,11 +402,19 @@ static int init_tdx_module(void)
if (ret)
goto out_free_tdxmem;

+ /* Allocate enough space for constructing TDMRs */
+ ret = alloc_tdmr_list(&tdmr_list, &tdmr_sysinfo);
+ if (ret)
+ goto out_free_tdxmem;
+
+ /* Cover all TDX-usable memory regions in TDMRs */
+ ret = construct_tdmrs(&tdx_memlist, &tdmr_list, &tdmr_sysinfo);
+ if (ret)
+ goto out_free_tdmrs;
+
/*
* TODO:
*
- * - Construct a list of TDMRs to cover all TDX-usable memory
- * regions.
* - Configure the TDMRs and the global KeyID to the TDX module.
* - Configure the global KeyID on all packages.
* - Initialize all TDMRs.
@@ -338,6 +422,12 @@ static int init_tdx_module(void)
* Return error before all steps are done.
*/
ret = -EINVAL;
+out_free_tdmrs:
+ /*
+ * Always free the buffer of TDMRs as they are only used during
+ * module initialization.
+ */
+ free_tdmr_list(&tdmr_list);
out_free_tdxmem:
if (ret)
free_tdx_memlist(&tdx_memlist);
diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
index 29cdf5ea5544..9b6b5d70804f 100644
--- a/arch/x86/virt/vmx/tdx/tdx.h
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -47,6 +47,30 @@

#define MD_FIELD_ID_ELE_SIZE_16BIT 1

+struct tdmr_reserved_area {
+ u64 offset;
+ u64 size;
+} __packed;
+
+#define TDMR_INFO_ALIGNMENT 512
+
+struct tdmr_info {
+ u64 base;
+ u64 size;
+ u64 pamt_1g_base;
+ u64 pamt_1g_size;
+ u64 pamt_2m_base;
+ u64 pamt_2m_size;
+ u64 pamt_4k_base;
+ u64 pamt_4k_size;
+ /*
+ * The actual number of reserved areas depends on the value of
+ * field MD_FIELD_ID_MAX_RESERVED_PER_TDMR in the TDX module
+ * global metadata.
+ */
+ DECLARE_FLEX_ARRAY(struct tdmr_reserved_area, reserved_areas);
+} __packed __aligned(TDMR_INFO_ALIGNMENT);
+
/*
* Do not put any hardware-defined TDX structure representations below
* this comment!
@@ -72,4 +96,13 @@ struct tdx_tdmr_sysinfo {
u16 pamt_entry_size[TDX_PS_NR];
};

+struct tdmr_info_list {
+ void *tdmrs; /* Flexible array to hold 'tdmr_info's */
+ int nr_consumed_tdmrs; /* How many 'tdmr_info's are in use */
+
+ /* Metadata for finding target 'tdmr_info' and freeing @tdmrs */
+ int tdmr_sz; /* Size of one 'tdmr_info' */
+ int max_tdmrs; /* How many 'tdmr_info's are allocated */
+};
+
#endif
--
2.41.0