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| author | Jeremy Fitzhardinge | 2008-01-30 13:32:59 +0100 |
|---|---|---|
| committer | Ingo Molnar | 2008-01-30 13:32:59 +0100 |
| commit | f29192320f22f1617d50a9c790862603eeef64e6 (patch) | |
| tree | c496f893ee5d4e8c9636756483411a6ef46c6721 /arch/x86/kernel/cpu/mcheck/mce_64.c | |
| parent | xen: mask out PWT too (diff) | |
| download | kernel-qcow2-linux-f29192320f22f1617d50a9c790862603eeef64e6.tar.gz kernel-qcow2-linux-f29192320f22f1617d50a9c790862603eeef64e6.tar.xz kernel-qcow2-linux-f29192320f22f1617d50a9c790862603eeef64e6.zip | |
x86/pgtable: explain constant sign extension problem
When the _PAGE_FOO constants are defined as (1ul << _PAGE_BIT_FOO), they
become unsigned longs. In 32-bit PAE mode, these end up being
implicitly cast to 64-bit types when used to manipulate a pte, and
because they're unsigned the top 32-bits are 0, destroying the upper
bits of the pte.
When _PAGE_FOO constants are given a signed integer type, the cast to
64-bits will sign-extend so that the upper bits are all ones,
preserving the upper pte bits in manipulations.
Explain this in a prominent place.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch/x86/kernel/cpu/mcheck/mce_64.c')
0 files changed, 0 insertions, 0 deletions