Commit 371b8044 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman

powerpc/64s: Initialize ISAv3 MMU registers before setting partition table

kexec can leave MMU registers set when booting into a new kernel,
the PIDR (Process Identification Register) in particular. The boot
sequence does not zero PIDR, so it only gets set when CPUs first
switch to a userspace processes (until then it's running a kernel
thread with effective PID = 0).

This leaves a window where a process table entry and page tables are
set up due to user processes running on other CPUs, that happen to
match with a stale PID. The CPU with that PID may cause speculative
accesses that address quadrant 0 (aka userspace addresses), which will
result in cached translations and PWC (Page Walk Cache) for that
process, on a CPU which is not in the mm_cpumask and so they will not
be invalidated properly.

The most common result is the kernel hanging in infinite page fault
loops soon after kexec (usually in schedule_tail, which is usually the
first non-speculative quadrant 0 access to a new PID) due to a stale
PWC. However being a stale translation error, it could result in
anything up to security and data corruption problems.

Fix this by zeroing out PIDR at boot and kexec.

Fixes: 7e381c0f ("powerpc/mm/radix: Add mmu context handling callback for radix")
Cc: stable@vger.kernel.org # v4.7+
Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent ab9dbf77
...@@ -102,6 +102,7 @@ _GLOBAL(__setup_cpu_power9) ...@@ -102,6 +102,7 @@ _GLOBAL(__setup_cpu_power9)
li r0,0 li r0,0
mtspr SPRN_PSSCR,r0 mtspr SPRN_PSSCR,r0
mtspr SPRN_LPID,r0 mtspr SPRN_LPID,r0
mtspr SPRN_PID,r0
mfspr r3,SPRN_LPCR mfspr r3,SPRN_LPCR
LOAD_REG_IMMEDIATE(r4, LPCR_PECEDH | LPCR_PECE_HVEE | LPCR_HVICE | LPCR_HEIC) LOAD_REG_IMMEDIATE(r4, LPCR_PECEDH | LPCR_PECE_HVEE | LPCR_HVICE | LPCR_HEIC)
or r3, r3, r4 or r3, r3, r4
...@@ -126,6 +127,7 @@ _GLOBAL(__restore_cpu_power9) ...@@ -126,6 +127,7 @@ _GLOBAL(__restore_cpu_power9)
li r0,0 li r0,0
mtspr SPRN_PSSCR,r0 mtspr SPRN_PSSCR,r0
mtspr SPRN_LPID,r0 mtspr SPRN_LPID,r0
mtspr SPRN_PID,r0
mfspr r3,SPRN_LPCR mfspr r3,SPRN_LPCR
LOAD_REG_IMMEDIATE(r4, LPCR_PECEDH | LPCR_PECE_HVEE | LPCR_HVICE | LPCR_HEIC) LOAD_REG_IMMEDIATE(r4, LPCR_PECEDH | LPCR_PECE_HVEE | LPCR_HVICE | LPCR_HEIC)
or r3, r3, r4 or r3, r3, r4
......
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