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SubjectRe: [PATCH] x86, pkeys: update documentation about availability

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

> On 11/09/2017 10:12 PM, Ingo Molnar wrote:
> >
> > * Dave Hansen <dave.hansen@linux.intel.com> wrote:
> >
> >>
> >> From: Dave Hansen <dave.hansen@linux.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@linux.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

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