linux-kernel - Re: [PATCH] x86, pkeys: update documentation about availability

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Date:   Thu, 9 Nov 2017 22:41:32 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86, pkeys: update documentation about availability

On 11/09/2017 10:12 PM, Ingo Molnar wrote:
> 
> * Dave Hansen <dave.hansen@...ux.intel.com> wrote:
> 
>>
>> From: Dave Hansen <dave.hansen@...ux.intel.com>
>>
>> Now that CPUs that implement Memory Protection Keys are publicly
>> available we can be a bit less oblique about where it is available.
>>
>> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
>> ---
>>
>>  b/Documentation/x86/protection-keys.txt |    9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff -puN Documentation/x86/protection-keys.txt~pkeys-update Documentation/x86/protection-keys.txt
>> --- a/Documentation/x86/protection-keys.txt~pkeys-update	2017-11-09 10:36:53.381467202 -0800
>> +++ b/Documentation/x86/protection-keys.txt	2017-11-09 10:43:15.527466249 -0800
>> @@ -1,5 +1,10 @@
>> -Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature
>> -which will be found on future Intel CPUs.
>> +Memory Protection Keys for Userspace (PKU aka PKEYs) is a feature
>> +which is found on Intel's Skylake "Scalable Processor" Server CPUs.
>> +It will be avalable in future non-server parts.
>> +
>> +For anyone wishing to test or use this feature, it is available in
>> +Amazon's EC2 C5 instances and is known to work there using an Ubuntu
>> +17.04 image.
>>  
>>  Memory Protection Keys provides a mechanism for enforcing page-based
>>  protections, but without requiring modification of the page tables
> 
> Could we please first fix the pkeys self-test? One of the testcases doesn't build 
> at all:
> 
>  gcc -m32 -o /home/mingo/tip/tools/testing/selftests/x86/protection_keys_32 -O2 -g -std=gnu99 -pthread -Wall -no-pie  protection_keys.c -lrt -ldl -lm
>  In file included from /usr/include/signal.h:57:0,
>                   from protection_keys.c:33:
>  protection_keys.c: In function ‘signal_handler’:
>  protection_keys.c:253:6: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ 
>  before ‘.’ token
>    u64 si_pkey;

That's odd.  I build them all the time.  I compiled it just now with
4.14-rc8 and gcc 4.8.4.

I wonder if this is more fallout from the glibc headers getting updated
to now contain pkey-related stuff.  si_pkey might be getting #defined
over for the siginfo si_pkey.

What distro are you seeing this on?

> plus, on a related note, the MPX testcase produces annoying warnings:
> 
>  gcc -m32 -o /home/mingo/tip/tools/testing/selftests/x86/mpx-mini-test_32 -O2 -g -std=gnu99 -pthread -Wall -no-pie  mpx-mini-test.c -lrt -ldl -lm
>  mpx-mini-test.c: In function ‘insn_test_failed’:
>  mpx-mini-test.c:1406:3: warning: array subscript is above array bounds 
>  [-Warray-bounds]
>     printf("bte[1]: %lx\n", bte->contents[1]);

This is kinda a weird structure:

> struct mpx_bt_entry {
>         union {
>                 char x[MPX_BOUNDS_TABLE_ENTRY_SIZE_BYTES];
>                 unsigned long contents[1];
>         };
> } __attribute__((packed));

I guess it should either be contents[0] or
contents[MPX_BOUNDS_TABLE_ENTRY_SIZE_BYTE/sizeof(long)].  But, the
warning is harmless at least.

What gcc is this, btw?  I must be behind the times.