Revision - b03897c - powerpc/powernv: Fix save/restore of SPRG3 on entry/exit from [...] - origin: https://github.com/torvalds/linux

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13 August 2024, 17:29:01 UTC

Revision b03897cf318dfc47de33a7ecbc7655584266f034 authored by Gautham R. Shenoy on 18 July 2018, 08:33:16 UTC, committed by Michael Ellerman on 18 July 2018, 10:40:17 UTC

powerpc/powernv: Fix save/restore of SPRG3 on entry/exit from stop (idle)

On 64-bit servers, SPRN_SPRG3 and its userspace read-only mirror
SPRN_USPRG3 are used as userspace VDSO write and read registers
respectively.

SPRN_SPRG3 is lost when we enter stop4 and above, and is currently not
restored.  As a result, any read from SPRN_USPRG3 returns zero on an
exit from stop4 (Power9 only) and above.

Thus in this situation, on POWER9, any call from sched_getcpu() always
returns zero, as on powerpc, we call __kernel_getcpu() which relies
upon SPRN_USPRG3 to report the CPU and NUMA node information.

Fix this by restoring SPRN_SPRG3 on wake up from a deep stop state
with the sprg_vdso value that is cached in PACA.

Fixes: e1c1cfed5432 ("powerpc/powernv: Save/Restore additional SPRs for stop4 cpuidle")
Cc: stable@vger.kernel.org # v4.14+
Reported-by: Florian Weimer <fweimer@redhat.com>
Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Reviewed-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 parent 4e4a4b7

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Tip revision: b03897cf318dfc47de33a7ecbc7655584266f034 authored by Gautham R. Shenoy on 18 July 2018, 08:33:16 UTC
powerpc/powernv: Fix save/restore of SPRG3 on entry/exit from stop (idle)

Tip revision: b03897c

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powerpc/powernv: Fix save/restore of SPRG3 on entry/exit from stop (idle)

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