| Message ID | 20220510111809.15987-1-graf@amazon.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] KVM: PPC: Book3S PR: Enable MSR_DR for switch_mmu_context() | expand |
Le 10/05/2022 à 13:18, 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. Is the system ready to handle a DSI in case the stack is not mapped ? > > 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@ozlabs.org> > Fixes: 863771a28e27 ("powerpc/32s: Convert switch_mmu_context() to C") Oops, sorry for that. I didn't realise that there was other callers to switch_mmu_context() than switch_mm_irqs_off(). Christophe > 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. > --- > 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
On 10.05.22 13:31, Christophe Leroy wrote: > Le 10/05/2022 à 13:18, 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. > Is the system ready to handle a DSI in case the stack is not mapped ? A DSI itself will be an interrupt again which will in turn destroy the SPRG that we're saving. Guess I was trying to be too smart :). I'll use Matt's original suggestion and just put it on the stack. >> 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@ozlabs.org> >> Fixes: 863771a28e27 ("powerpc/32s: Convert switch_mmu_context() to C") > Oops, sorry for that. I didn't realise that there was other callers to > switch_mmu_context() than switch_mm_irqs_off(). No worries, the compiled C version looks a lot nicer than the previous asm one - and it was a good way to identify whether there still are users of KVM on Book3S 32bit out there :) Alex 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..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
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@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. --- arch/powerpc/kvm/book3s_32_sr.S | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-)