linux-kernel - Re: [PATCH] x86/sgx: Add SGX

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Date:   Wed, 18 Aug 2021 16:40:26 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Jethro Beekman <jethro@...tanix.com>
Cc:     linux-sgx@...r.kernel.org, Shuah Khan <shuah@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Jonathan Corbet <corbet@....net>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Saravanan D <saravanand@...com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Krish Sadhukhan <krish.sadhukhan@...cle.com>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH] x86/sgx: Add SGX_MemTotal to /proc/meminfo

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@...nel.org>
> > ---
> >  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.

/Jarkko