MIPS: Add missing EHB in mtc0 -> mfc0 sequence.
commit 0b24cae4d535045f4c9e177aa228d4e97bad212c upstream. Add a missing EHB (Execution Hazard Barrier) in mtc0 -> mfc0 sequence. Without this execution hazard barrier it's possible for the value read back from the KScratch register to be the value from before the mtc0. Reproducible on P5600 & P6600. The hazard is documented in the MIPS Architecture Reference Manual Vol. III: MIPS32/microMIPS32 Privileged Resource Architecture (MD00088), rev 6.03 table 8.1 which includes: Producer | Consumer | Hazard ----------|----------|---------------------------- mtc0 | mfc0 | any coprocessor 0 register Signed-off-by: NDmitry Korotin <dkorotin@wavecomp.com> [paul.burton@mips.com: - Commit message tweaks. - Add Fixes tags. - Mark for stable back to v3.15 where P5600 support was introduced.] Signed-off-by: NPaul Burton <paul.burton@mips.com> Fixes: 3d8bfdd0 ("MIPS: Use C0_KScratch (if present) to hold PGD pointer.") Fixes: 829dcc0a ("MIPS: Add MIPS P5600 probe support") Cc: linux-mips@vger.kernel.org Cc: stable@vger.kernel.org # v3.15+ Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
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