linux-kernel - Re: [PATCH v4 1/8] x86/sgx: Add /sys/kernel/debug/x86/sgx_total

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Date:   Fri, 13 Aug 2021 12:53:44 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Jarkko Sakkinen <jarkko@...nel.org>, Shuah Khan <shuah@...nel.org>
Cc:     linux-kselftest@...r.kernel.org, linux-sgx@...r.kernel.org,
        Reinette Chatre <reinette.chatre@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Jonathan Corbet <corbet@....net>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v4 1/8] x86/sgx: Add /sys/kernel/debug/x86/sgx_total_mem

On 8/9/21 3:31 AM, Jarkko Sakkinen wrote:
> Just like normal memory, SGX memory can be overcommitted.  SGX has its
> own reclaim mechanism which kicks in when physical SGX memory (Enclave
> Page Cache / EPC) is exhausted.  That reclaim mechanism is relatively
> rarely exercised and needs selftests to poke at it.
> 
> The amount of EPC on the system is determined by the BIOS and it varies
> wildly between systems.  It can be dozens of MB on desktops, or many GB
> on servers.
> 
> To run in a reasonable amount of time, the selftest needs to know how
> much EPC there is in the system.
> 
> Introduce a new debugfs file to export that information.
> 
> Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
> ---
> 
> v3:
> * Describe the units of sgx_total_mem in Dcumentation/x86/sgx.rst.
> * Rewrite of the commit message (suggested by Dave):
>    https://lore.kernel.org/linux-sgx/5d3614af-2393-6744-9d85-7001241ca76e@intel.com/
> 
> v2:
> * sgx_nr_all_pages -> sgx_total_mem
> 
>   Documentation/x86/sgx.rst      |  6 ++++++
>   arch/x86/kernel/cpu/sgx/main.c | 10 +++++++++-
>   2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/x86/sgx.rst b/Documentation/x86/sgx.rst
> index dd0ac96ff9ef..f11bfb331b93 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.
> +
> +Debugging
> +=========
> +
> +*/sys/kernel/debug/x86/sgx_total_mem* contains an integer describing
> +the total SGX reserved memory in bytes, available in the system.
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 63d3de02bbcc..b65da19a53ee 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -1,6 +1,7 @@
>   // SPDX-License-Identifier: GPL-2.0
>   /*  Copyright(c) 2016-20 Intel Corporation. */
>   
> +#include <linux/debugfs.h>
>   #include <linux/file.h>
>   #include <linux/freezer.h>
>   #include <linux/highmem.h>
> @@ -28,7 +29,10 @@ static DECLARE_WAIT_QUEUE_HEAD(ksgxd_waitq);
>   static LIST_HEAD(sgx_active_page_list);
>   static DEFINE_SPINLOCK(sgx_reclaimer_lock);
>   
> -/* The free page list lock protected variables prepend the lock. */
> +/* Total EPC memory available in bytes. */
> +static unsigned long sgx_total_mem;
> +
> +/* 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 +660,8 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
>   		list_add_tail(&section->pages[i].list, &sgx_dirty_page_list);
>   	}
>   
> +	sgx_total_mem += nr_pages * PAGE_SIZE;
> +
>   	return true;
>   }
>   
> @@ -823,6 +829,8 @@ static int __init sgx_init(void)
>   	if (sgx_vepc_init() && ret)
>   		goto err_provision;
>   
> +	debugfs_create_ulong("sgx_total_mem", 0444, arch_debugfs_dir, &sgx_total_mem);

dbugfs init dependency would be met I assume by this time?

> +
>   	return 0;
>   
>   err_provision:
>