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f36ef40762
Patch series "selftests/vm/pkeys: Bug fixes and a new test".
There has been a lot of activity on the x86 front around the XSAVE
architecture which is used to context-switch processor state (among other
things). In addition, AMD has recently joined the protection keys club by
adding processor support for PKU.
The AMD implementation helped uncover a kernel bug around the PKRU "init
state", which actually applied to Intel's implementation but was just
harder to hit. This series adds a test which is expected to help find
this class of bug both on AMD and Intel. All the work around pkeys on x86
also uncovered a few bugs in the selftest.
This patch (of 4):
The "random" pkey allocation code currently does the good old:
srand((unsigned int)time(NULL));
*But*, it unfortunately does this on every random pkey allocation.
There may be thousands of these a second. time() has a one second
resolution. So, each time alloc_random_pkey() is called, the PRNG is
*RESET* to time(). This is nasty. Normally, if you do:
srand(<ANYTHING>);
foo = rand();
bar = rand();
You'll be quite guaranteed that 'foo' and 'bar' are different. But, if
you do:
srand(1);
foo = rand();
srand(1);
bar = rand();
You are quite guaranteed that 'foo' and 'bar' are the *SAME*. The recent
"fix" effectively forced the test case to use the same "random" pkey for
the whole test, unless the test run crossed a second boundary.
Only run srand() once at program startup.
This explains some very odd and persistent test failures I've been seeing.
Link: https://lkml.kernel.org/r/20210611164153.91B76FB8@viggo.jf.intel.com
Link: https://lkml.kernel.org/r/20210611164155.192D00FF@viggo.jf.intel.com
Fixes:
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| .. | ||
| accounting | ||
| arch | ||
| bootconfig | ||
| bpf | ||
| build | ||
| cgroup | ||
| debugging | ||
| edid | ||
| firewire | ||
| firmware | ||
| gpio | ||
| hv | ||
| iio | ||
| include | ||
| io_uring | ||
| kvm/kvm_stat | ||
| laptop | ||
| leds | ||
| lib | ||
| memory-model | ||
| objtool | ||
| pci | ||
| pcmcia | ||
| perf | ||
| power | ||
| scripts | ||
| spi | ||
| testing | ||
| thermal/tmon | ||
| time | ||
| tracing | ||
| usb | ||
| virtio | ||
| vm | ||
| wmi | ||
| Makefile | ||