Re: [PATCH v2 1/4] x86/sgx: Add /sys/kernel/debug/x86/sgx_total_mem

Jarkko Sakkinen
2021-07-30T00:59:37Z

On Thu, Jul 29, 2021 at 09:27:41AM -0700, Dave Hansen wrote:
> On 7/28/21 3:51 PM, Jarkko Sakkinen wrote:
> > Create /sys/kernel/debug/x86/sgx_total_mem, after the driver is
> > initialized, describing the total amount of SGX reserved memory (also known
> > as Enclave Page Cache (EPC)) available in the system.
> >
> > This can be used to implement stress that trigger the page reclaimer, and
> > it is probably useful information when admistering a system running
> > enclaves anyhow.
>
> How about this as a rewrite?
>
> 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.
>
> > diff --git a/Documentation/x86/sgx.rst b/Documentation/x86/sgx.rst
> > index dd0ac96ff9ef..15bb8f4e42af 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.
> > +
> > +SGX debugging
> > +=============
> > +
> > +*/sys/kernel/debug/x86/sgx_total_mem* describes the total available
> > +SGX mwemory available in the system.
>
> ^ memory
>
> It would also be nice to say what the units are here, even if they are
> bytes.
>
> > 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);
> > +
> > return 0;
> >
> > err_provision:
> >
>
> Assuming the new changelog is adopted and typos fixed:
>
> Acked-by: Dave Hansen <dave.hansen@linux.intel.com>

Thanks, I'll commit these changes and include to the next version.

/Jarkko