| Message ID | 20220509202355.13985-1-graf@amazon.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: PPC: Book3S PR: Enable MSR_DR for switch_mmu_context() | expand |
Hi Alex, > On 9 May 2022, at 21:23, Alexander Graf <graf@amazon.com> wrote: > > 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. > > 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 Many thanks - this addresses the issue I saw, and has been... Tested-by: Matt Evans <matt@ozlabs.org> ...on a G4 host. One comment though: > — > arch/powerpc/kvm/book3s_32_sr.S | 20 +++++++++++++++----- > 1 file changed, 15 insertions(+), 5 deletions(-) > > diff --git a/arch/powerpc/kvm/book3s_32_sr.S b/arch/powerpc/kvm/book3s_32_sr.S > index e3ab9df6cf19..bd4f798f7a46 100644 > --- a/arch/powerpc/kvm/book3s_32_sr.S > +++ b/arch/powerpc/kvm/book3s_32_sr.S > @@ -122,11 +122,21 @@ > > /* 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 > + > + /* Calling switch_mmu_context(<inv>, current->mm, <inv>); */ > + lwz r4, MM(r2) > bl switch_mmu_context Of the volatile registers, I believe r12 is still valuable here and would need to be preserved. (I can’t spot any others but would defer to your judgement here.) For example: diff --git a/arch/powerpc/kvm/book3s_32_sr.S b/arch/powerpc/kvm/book3s_32_sr.S index e3ab9df6cf19..41fc9ca12d38 100644 --- a/arch/powerpc/kvm/book3s_32_sr.S +++ b/arch/powerpc/kvm/book3s_32_sr.S @@ -122,11 +122,23 @@ /* 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 + + SAVE_GPR(12, r1) + /* Calling switch_mmu_context(<inv>, current->mm, <inv>); */ + lwz r4, MM(r2) bl switch_mmu_context + REST_GPR(12, r1) + + /* Disable paging again */ + mfmsr r9 + li r6, MSR_DR + andc r9, r9, r6 + mtmsr r9 + sync .endm Matt > > + /* Disable paging again */ > + mfmsr r9 > + li r6, MSR_DR > + andc r9, r9, r6 > + mtmsr r9 > + sync > + > .endm > -- > 2.28.0.394.ge197136389 > > > > > Amazon Development Center Germany GmbH > Krausenstr. 38 > 10117 Berlin > Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss > Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B > Sitz: Berlin > Ust-ID: DE 289 237 879 > > >
diff --git a/arch/powerpc/kvm/book3s_32_sr.S b/arch/powerpc/kvm/book3s_32_sr.S index e3ab9df6cf19..bd4f798f7a46 100644 --- a/arch/powerpc/kvm/book3s_32_sr.S +++ b/arch/powerpc/kvm/book3s_32_sr.S @@ -122,11 +122,21 @@ /* 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 + + /* 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 + .endm
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. 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 --- arch/powerpc/kvm/book3s_32_sr.S | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-)