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

[Shuah Khan]

On 8/18/21 7:40 AM, Jarkko Sakkinen wrote:
> On Wed, Aug 18, 2021 at 03:29:59PM +0200, Jethro Beekman wrote:
> > On 2021-08-18 15:25, 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@xxxxxxxxxx>
> > > ---
> > >   Documentation/x86/sgx.rst      |  6 ++++++
> > >   arch/x86/include/asm/sgx.h     | 10 +++++++---
> > >   arch/x86/kernel/cpu/sgx/main.c |  7 ++++++-
> > >   arch/x86/mm/pat/set_memory.c   |  5 +++++
> > >   4 files changed, 24 insertions(+), 4 deletions(-)
> > >
> > > 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.
> > > diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
> > > index 05f3e21f01a7..2ae9dc8c9411 100644
> > > --- a/arch/x86/include/asm/sgx.h
> > > +++ b/arch/x86/include/asm/sgx.h
> > > @@ -365,6 +365,13 @@ struct sgx_sigstruct {
> > >    * comment!
> > >    */
> > >   
> > > +#if defined(CONFIG_X86_SGX) || defined(CONFIG_X86_SGX_KVM)
> > > +extern unsigned long sgx_nr_all_pages;
> > > +
> > > +int sgx_set_attribute(unsigned long *allowed_attributes,
> > > +		      unsigned int attribute_fd);
> > > +#endif
> > > +
> > >   #ifdef CONFIG_X86_SGX_KVM
> > >   int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo, void __user *secs,
> > >   		     int *trapnr);
> > > @@ -372,7 +379,4 @@ int sgx_virt_einit(void __user *sigstruct, void __user *token,
> > >   		   void __user *secs, u64 *lepubkeyhash, int *trapnr);
> > >   #endif
> > >   
> > > -int sgx_set_attribute(unsigned long *allowed_attributes,
> > > -		      unsigned int attribute_fd);
> > > -
> >
> > This change seems unrelated?
>
> It's just a good practice not to define symbols that do not exist, so that
> if the symbol is ever used, we get a compilation error, not linking error.
>
> Since this is included to set_memory.c, based on this conclusion, I added
> the check.

It would make sense to make this change in a separate patch since.

thanks,
-- Shuah