Re: [PATCH 3/3] KVM: PPC: Book3S: 64-bit CONFIG_RELOCATABLE support for interrupts
From: Paul Mackerras <hidden>
Date: 2017-01-31 08:02:01
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@gmail.com>
Unfortunately, this patch causes guests to crash in various ways when running under a CONFIG_RELOCATABLE kernel. See below...
quoted hunk ↗ jump to hunk
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. Paul.