linux-kernel - Re: XSAVE / RDPKRU on Intel 11th Gen Core CPUs

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Date:   Mon, 8 Nov 2021 20:47:39 -0500
From:   Brian Geffon <bgeffon@...gle.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Guenter Roeck <groeck@...gle.com>,
        Borislav Petkov <bp@...e.de>,
        Andy Lutomirski <luto@...nel.org>, stable@...r.kernel.org,
        "the arch/x86 maintainers" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: XSAVE / RDPKRU on Intel 11th Gen Core CPUs

> One more thing...  Does the protection_keys kernel selftest hit any
> errors on this same setup?  It does a lot of PKRU sanity checking and
> I'm a bit surprised it hasn't caught something yet.

Hi Dave,

This issue does reproduce with the self tests too, my simple test
program also fails consistently [1], all it does is spin executing
RDPKRU waiting for a context switch to clobber the value.

$ ./test
unexpected value on iteration 3772082 value:0x55555554 expected:0x55555550

==========================
self tests:

$ ./protection_keys_64
has pkeys: 1
startup pkey_reg: 0000000055555550
WARNING: not run as root, can not do hugetlb test
test 0 PASSED (iteration 1)
test 1 PASSED (iteration 1)
test 2 PASSED (iteration 1)
test 3 PASSED (iteration 1)
test 4 PASSED (iteration 1)
test 5 PASSED (iteration 1)
protection_keys_64: pkey-helpers.h:127: _read_pkey_reg: Assertion
`pkey_reg == shadow_pkey_reg' failed.
Aborted (core dumped)

$ uname -a
Linux localhost 5.13.0-17189-g62fb9874f5da #12 SMP PREEMPT Tue Nov 9
01:29:44 UTC 2021 x86_64 11th Gen Intel(R) Core(TM) i5-1135G7 @
2.40GHz GenuineIntel GNU/Linux

Let me know if I can provide anything else, I'm happy to help troubleshoot this.

Thanks,
Brian

1. https://gist.github.com/bgaff/e4b5457ab1cf5126fea6327666c63441