Messages in this thread | | | Date | Wed, 8 Dec 2021 11:10:31 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v13 2/2] x86/sgx: Add an attribute for the amount of SGX memory in a NUMA node |
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On Tue, Dec 07, 2021 at 11:36:50AM -0800, Dave Hansen wrote: > On 11/16/21 8:21 AM, 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. > > > > Introduce CONFIG_HAVE_ARCH_NODE_DEV_GROUP opt-in flag to expose an arch > > specific attribute group, and add an attribute for the amount of SGX > > memory in bytes to each NUMA node: > > > > /sys/devices/system/node/nodeX/x86/sgx_total_bytes > > There's some context missing here:
I'll say. "it is sometimes useful" is not the proper argumentation for adding new stuff.
> This serves the same function for SGX memory as /proc/meminfo or > /sys/devices/system/node/nodeX/meminfo does for normal RAM. It > enumerates how much physical SGX memory is present so that you can size > enclaves on different systems. > > This specific file (sgx_total_bytes) is needed today to help drive the > SGX selftests. The SGX selftests need to create overcommitted enclaves > which are larger than the physical SGX memory on the system. They > currently use a CPUID-based approach which can diverge from the actual > amount of SGX memory available. This file ensures that the selftests > can work efficiently and do not attempt stupid things like creating a > 100,000 MB enclave on a system with 128 MB of SGX memory.
Thanks, that's exactly what I was missing. Please stick that explanation somewhere prominent.
> The nodeX/x86 directory is used because SGX is highly x86-specific. > It's very unlikely that any other architecture (or even non-Intel x86 > vendor) will ever implement SGX. It needs its own directory (as opposed > to being in the nodeX/ "root") because this is expected to be the first > of a few different things that need to get exported. This avoids > cluttering the root with several "sgx_*" files. > > How many of these files will there be? Just scanning /proc/meminfo, > these are the no-brainers that we have for RAM, but we need for SGX: > > MemTotal: xxxx kB // sgx_total_bytes (this patch) > MemFree: yyyy kB // sgx_free_bytes > SwapTotal: zzzz kB // sgx_swapped_bytes > > So, at *least* three. I think we will eventually end up needing > something more along the lines of a dozen.
Oh well, I guess.
I was going to propose to make that
...nodeX/sgx/
but having it be arch-specific would mean that theoretically we could add some non-sgx files there too, in the future, and if/when needed.
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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