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    Subject[PATCH 5.15 064/102] KVM: PPC: Book3S PR: Enable MSR_DR for switch_mmu_context()
    Date
    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(-)

    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
    + mtmsr r9
    + sync
    +
    .endm
    --
    2.36.1


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