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

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Message-ID: <20171110071723.p3wy6pth57iibwoe@gmail.com>
Date:   Fri, 10 Nov 2017 08:17:23 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
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


* Dave Hansen <dave.hansen@...ux.intel.com> wrote:

> 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?

Latest Ubuntu, 17.10:

  triton:~/tip> cat /etc/os-release 
  NAME="Ubuntu"
  VERSION="17.10 (Artful Aardvark)"

  triton:~/tip> apt-file find /usr/include/signal.h
  libc6-dev: /usr/include/signal.h

  triton:~/tip> dpkg -l libc6-dev
  Desired=Unknown/Install/Remove/Purge/Hold
  | Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
  |/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
  ||/ Name                                    Version                  Architecture             Description
  +++-=======================================-========================-========================-====================================================================================
  ii  libc6-dev:amd64                         2.26-0ubuntu2            amd64                    GNU C Library: Development Libraries and Header Files


> > 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.

gcc version 7.2.0 (Ubuntu 7.2.0-8ubuntu3) 

Thanks,

	Ingo