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

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Date:   Thu, 19 Aug 2021 14:32:45 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Shuah Khan <skhan@...uxfoundation.org>,
        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, 2021-08-18 at 12:34 -0600, Shuah Khan wrote:
> 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@...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.
> > 
> 
> It would make sense to make this change in a separate patch since.
> 
> thanks,
> -- Shuah

NP, I can split it.

/Jarkko