Le 10/05/2022 à 14:37, Alexander Graf a écrit :

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.

Reported-by: Matt Evans matt@ozlabs.org Fixes: 863771a28e27 ("powerpc/32s: Convert switch_mmu_context() to C") Signed-off-by: Alexander Graf graf@amazon.com Cc: stable@vger.kernel.org # v5.14+

---

v1 -> v2:

• Save and restore R12, so that we don't touch volatile registers while calling into C.

v2 -> v3:

• Save and restore R12 on the stack. SPRGs may be clobbered by page faults.

---

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..6cfcd20d4668 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() 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

Instead of li/andc you can do:

rlwinm r9, r9, 0, ~MSR_DR

• mtmsr r9
• sync
• .endm