Commit 863771a28e27 ("powerpc/32s: Convert switch_mmu_context() to C")
moved the switch_mmu_context() to C. While in principle a good idea, it
meant that the function now uses the stack. The stack is not accessible
from real mode though.
So to keep calling the function, let's turn on MSR_DR while we call it.
That way, all pointer references to the stack are handled virtually.
In addition, make sure to save/restore r12 in an SPRG, as it may get
clobbered by the C function.
Reported-by: Matt Evans <matt@xxxxxxxxxx>
Fixes: 863771a28e27 ("powerpc/32s: Convert switch_mmu_context() to C")
Signed-off-by: Alexander Graf <graf@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v5.14+
---
v1 -> v2:
- Save and restore R12, so that we don't touch volatile registers
while calling into C.
---
arch/powerpc/kvm/book3s_32_sr.S | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_32_sr.S b/arch/powerpc/kvm/book3s_32_sr.S
index e3ab9df6cf19..1ce13e3ab072 100644
--- a/arch/powerpc/kvm/book3s_32_sr.S
+++ b/arch/powerpc/kvm/book3s_32_sr.S
@@ -122,11 +122,27 @@
/* 0x0 - 0xb */
- /* 'current->mm' needs to be in r4 */
- tophys(r4, r2)
- lwz r4, MM(r4)
- tophys(r4, r4)
- /* This only clobbers r0, r3, r4 and r5 */
+ /* switch_mmu_context() clobbers r12, rescue it */
+ SET_SCRATCH0(r12)
+
+ /* switch_mmu_context() needs paging, let's enable it */
+ mfmsr r9
+ ori r11, r9, MSR_DR
+ mtmsr r11
+ sync
+
+ /* Calling switch_mmu_context(<inv>, current->mm, <inv>); */
+ lwz r4, MM(r2)
bl switch_mmu_context
+ /* Disable paging again */
+ mfmsr r9
+ li r6, MSR_DR
+ andc r9, r9, r6
+ mtmsr r9
+ sync
+
+ /* restore r12 */
+ GET_SCRATCH0(r12)
+
.endm
--
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