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

[Jarkko Sakkinen <jarkko@kernel.org>]

On Wed, 2021-08-25 at 17:39 -0700, Randy Dunlap wrote:
> On 8/25/21 4:52 PM, Jarkko Sakkinen wrote:
> > 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