[PATCH 5.17 072/114] KVM: PPC: Book3S PR: Enable MSR_DR for switch_mmu_context()

Greg Kroah-Hartman
2022-05-16T20:32:47Z

From: Alexander Graf <graf@amazon.com>

commit ee8348496c77e3737d0a6cda307a521f2cff954f upstream.

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 on the stack, as it may get
clobbered by the C function.

Fixes: 863771a28e27 ("powerpc/32s: Convert switch_mmu_context() to C")
Cc: stable@vger.kernel.org # v5.14+
Reported-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Alexander Graf <graf@amazon.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220510123717.24508-1-graf@amazon.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/kvm/book3s_32_sr.S | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)

--- 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() needs paging, let's enable it */
+ mfmsr r9
+ ori r11, r9, MSR_DR
+ mtmsr r11
+ sync
+
+ /* switch_mmu_context() clobbers r12, rescue it */
+ SAVE_GPR(12, r1)
+
+ /* Calling switch_mmu_context(<inv>, current->mm, <inv>); */
+ lwz r4, MM(r2)
bl switch_mmu_context

+ /* restore r12 */
+ REST_GPR(12, r1)
+
+ /* Disable paging again */
+ mfmsr r9
+ li r6, MSR_DR
+ andc r9, r9, r6
+ mtmsr r9
+ sync
+
.endm