Re: [PATCH v3 2/2] x86/sgx: Add SGX_MemTotal to /proc/meminfo

On Wed, 2021-08-25 at 17:39 -0700, Randy Dunlap wrote:

On 8/25/21 4:52 PM, Jarkko Sakkinen wrote:

quoted

The amount of SGX memory on the system is determined by the BIOS and it
varies wildly between systems.  It can be from dozens of MB's on desktops
or VM's, up to many GB's on servers.  Just like for regular memory, it is
sometimes useful to know the amount of usable SGX memory in the system.

Add SGX_MemTotal field to /proc/meminfo, which shows the total amount of
usable SGX memory in the system.  E.g. with 32 MB reserved for SGX from
BIOS, the printout would be:

SGX_MemTotal:      22528 kB

It is less than 32 MB because some of the space is reserved for Enclave
Page Cache Metadata (EPCM), which contains state variables for all the
pages in the Enclave Page Cache (EPC).  The latter contains the pages,
which applications can use to create enclaves.

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

---
v2:
* Move ifdef fix for sgx_set_attribute() to a separate patch.
---
  Documentation/x86/sgx.rst      | 6 ++++++
  arch/x86/include/asm/sgx.h     | 2 ++
  arch/x86/kernel/cpu/sgx/main.c | 7 ++++++-
  arch/x86/mm/pat/set_memory.c   | 5 +++++
  4 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/Documentation/x86/sgx.rst b/Documentation/x86/sgx.rst
index dd0ac96ff9ef..68ee171e1d8f 100644
--- a/Documentation/x86/sgx.rst
+++ b/Documentation/x86/sgx.rst

@@ -250,3 +250,9 @@ user wants to deploy SGX applications both on the host and in guests
  on the same machine, the user should reserve enough EPC (by taking out
  total virtual EPC size of all SGX VMs from the physical EPC size) for
  host SGX applications so they can run with acceptable performance.
+
+Supplemental fields for /proc/meminfo
+=====================================
+
+SGX_MemTotal
+	The total usable SGX protected memory in kilobytes.

Hi,

I would prefer to see this listed in Documentation/filesystems/proc.rst
as an optional field, depending on CONFIG_X86_SGX.
Or at least put a reference in proc.rst to this doc file and its
supplemental fields.

thanks.

I *can* put it there but I did have reason not to, i.e. these attributes
are neither there:

DirectMap4k:     3930904 kB
DirectMap2M:    29440000 kB
DirectMap1G:     1048576 kB

And they are implemented in arch specific code.

Actually they are undocumented, e.g.

$ git grep DirectMap4k
arch/powerpc/mm/book3s64/pgtable.c:     seq_printf(m, "DirectMap4k:    %8lu kB\n",
arch/s390/mm/pageattr.c:        seq_printf(m, "DirectMap4k:    %8lu kB\n",
arch/x86/mm/pat/set_memory.c:   seq_printf(m, "DirectMap4k:    %8lu kB\n",

/Jarkko