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

From: Jarkko Sakkinen <jarkko@kernel.org>
To: Kai Huang <kai.huang@intel.com>
Cc: linux-sgx@vger.kernel.org,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Shuah Khan <shuah@kernel.org>,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org
Subject: Re: [PATCH v3 2/2] x86/sgx: Add SGX_MemTotal to /proc/meminfo
Date: Thu, 02 Sep 2021 15:15:51 +0300	[thread overview]
Message-ID: <41e9b099f6492c389b3ed3bbe107d61804a307e9.camel@kernel.org> (raw)
In-Reply-To: <20210901174705.3b1a943ef8c4bb09323c6d76@intel.com>

On Wed, 2021-09-01 at 17:47 +1200, Kai Huang wrote:
> On Wed, 01 Sep 2021 08:41:12 +0300 Jarkko Sakkinen wrote:
> > On Wed, 2021-09-01 at 17:33 +1200, Kai Huang wrote:
> > > On Wed, 01 Sep 2021 05:02:45 +0300 Jarkko Sakkinen wrote:
> > > > On Sat, 2021-08-28 at 00:03 +1200, Kai Huang wrote:
> > > > > > > > -/* The free page list lock protected variables prepend the lock. */
> > > > > > > > +/* The number of usable EPC pages in the system. */
> > > > > > > > +unsigned long sgx_nr_all_pages;
> > > > > > > > +
> > > > > > > > +/* The number of free EPC pages in all nodes. */
> > > > > > > >  static unsigned long sgx_nr_free_pages;
> > > > > > > >  
> > > > > > > >  /* Nodes with one or more EPC sections. */
> > > > > > > > @@ -656,6 +659,8 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
> > > > > > > >  		list_add_tail(&section->pages[i].list, &sgx_dirty_page_list);
> > > > > > > >  	}
> > > > > > > >  
> > > > > > > > +	sgx_nr_all_pages += nr_pages;
> > > > > > > > +
> > > > > > > 
> > > > > > > EPC sections can be freed again in sgx_init() after they are successfully
> > > > > > > initialized, when any further initialization fails (i.e. when fails to create
> > > > > > > ksgxd, or fails to register /dev/sgx_provision).  In which case, I think
> > > > > > > sgx_nr_all_pages should also be cleared.  But current sgx_init() seems doesn't
> > > > > > > reset it.  Do you need to fix that too?
> > > > > > 
> > > > > > sgx_nr_all_pages tells just the total pages in the system, i.e. it's a constant.
> > > > > > 
> > > > > > Maybe a rename to "sgx_nr_total_pages" would be a good idea? Would match with
> > > > > > the meminfo field better too.
> > > > > 
> > > > > I don't have preference on name.  I just think if there's no actual user of
> > > > > EPC (when both driver and KVM SGX cannot be enabled), it's pointless to print
> > > > > number of EPC pages.
> > > > 
> > > > I'd presume that you refer to the code, which prints the number of *bytes* in
> > > > the system because code printing the number of pages does not exist in this
> > > > patch set.
> > > > 
> > > > I have troubles the decipher your statement.
> > > > 
> > > > You think that only if both the driver and KVM are *both* enabled, only then
> > > > it makes sense to have this information available for sysadmin?
> > > 
> > > Only if at least one of them is enabled.
> > 
> > OK, thank you, that does make sense.
> > 
> > What would happen if neither is enabled is that SGX_MemTotal would
> > state that there is zero bytes of EPC. 
> 
> This is the problem I pointed out at the beginning, that (if I read code
> correctly), it seems your current patch doesn't clear sgx_nr_all_pages when
> neither is enabled (in sgx_init() in sgx/main.c).

It's initialized to zero, so are you talking about fallback when something
fails?

/Jarkko