[PATCH 3/3] KVM: PPC: Book3S: 64-bit CONFIG_RELOCATABLE support for interrupts
Nicholas Piggin
npiggin at gmail.com
Tue Jan 31 21:21:43 AEDT 2017
On Tue, 31 Jan 2017 19:01:52 +1100
Paul Mackerras <paulus at ozlabs.org> wrote:
> On Thu, Dec 22, 2016 at 04:29:27AM +1000, Nicholas Piggin wrote:
> > 64-bit Book3S exception handlers must find the dynamic kernel base
> > to add to the target address when branching beyond __end_interrupts,
> > in order to support kernel running at non-0 physical address.
> >
> > Support this in KVM by branching with CTR, similarly to regular
> > interrupt handlers. The guest CTR saved in HSTATE_SCRATCH1 and
> > restored after the branch.
> >
> > Without this, the host kernel hangs and crashes randomly when it is
> > running at a non-0 address and a KVM guest is started.
> >
> > Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
>
> Unfortunately, this patch causes guests to crash in various ways when
> running under a CONFIG_RELOCATABLE kernel. See below...
>
> > diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > index 11882aac8216..c18ce740452b 100644
> > --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > @@ -1060,15 +1060,16 @@ kvmppc_interrupt_hv:
> > * R12 = (guest CR << 32) | interrupt vector
> > * R13 = PACA
> > * guest R12 saved in shadow VCPU SCRATCH0
> > + * guest CTR saved in shadow VCPU SCRATCH1 if RELOCATABLE
> > * guest R13 saved in SPRN_SCRATCH0
> > */
> > - std r9, HSTATE_SCRATCH1(r13)
> > + std r9, HSTATE_SCRATCH2(r13)
> > lbz r9, HSTATE_IN_GUEST(r13)
> > cmpwi r9, KVM_GUEST_MODE_HOST_HV
> > beq kvmppc_bad_host_intr
> > #ifdef CONFIG_KVM_BOOK3S_PR_POSSIBLE
> > cmpwi r9, KVM_GUEST_MODE_GUEST
> > - ld r9, HSTATE_SCRATCH1(r13)
> > + ld r9, HSTATE_SCRATCH2(r13)
> > beq kvmppc_interrupt_pr
> > #endif
> > /* We're now back in the host but in guest MMU context */
> > @@ -1088,7 +1089,7 @@ kvmppc_interrupt_hv:
> > std r6, VCPU_GPR(R6)(r9)
> > std r7, VCPU_GPR(R7)(r9)
> > std r8, VCPU_GPR(R8)(r9)
> > - ld r0, HSTATE_SCRATCH1(r13)
> > + ld r0, HSTATE_SCRATCH2(r13)
> > std r0, VCPU_GPR(R9)(r9)
> > std r10, VCPU_GPR(R10)(r9)
> > std r11, VCPU_GPR(R11)(r9)
> > @@ -1151,7 +1152,11 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> > 11: stw r3,VCPU_HEIR(r9)
> >
> > /* these are volatile across C function calls */
> > +#ifdef CONFIG_RELOCATABLE
> > + ld r3, HSTATE_SCRATCH1(r13)
>
> The problem is here. Depending on what sort of interrupt it is, we
> can end up going back to the guest via fast_guest_return, which
> doesn't reload CTR. Adding
>
> mtctr r3
>
> at this point makes things work.
Thanks for tracking it down. Not enough testing on my end, I'm
sorry.
Thanks,
Nick
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