On Thursday 12 November 2015 09:04 AM, David Gibson wrote: > On Wed, Nov 11, 2015 at 10:28:46PM +0530, Aravinda Prasad wrote: >> This patch modifies KVM to cause a guest exit with >> KVM_EXIT_NMI instead of immediately delivering a 0x200 >> interrupt to guest upon machine check exception in >> guest address. Exiting the guest enables QEMU to build >> error log and deliver machine check exception to guest >> OS (either via guest OS registered machine check >> handler or via 0x200 guest OS interrupt vector). >> >> This approach simplifies the delivering of machine >> check exception to guest OS compared to the earlier approach >> of KVM directly invoking 0x200 guest interrupt vector. >> In the earlier approach QEMU patched the 0x200 interrupt >> vector during boot. The patched code at 0x200 issued a >> private hcall to pass the control to QEMU to build the >> error log. >> >> This design/approach is based on the feedback for the >> QEMU patches to handle machine check exception. Details >> of earlier approach of handling machine check exception >> in QEMU and related discussions can be found at: >> >> https://lists.nongnu.org/archive/html/qemu-devel/2014-11/msg00813.html >> >> Signed-off-by: Aravinda Prasad <aravi...@linux.vnet.ibm.com> >> --- >> arch/powerpc/kvm/book3s_hv.c | 12 +++--------- >> arch/powerpc/kvm/book3s_hv_rmhandlers.S | 31 >> +++++++++++-------------------- >> 2 files changed, 14 insertions(+), 29 deletions(-) >> >> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c >> index 2280497..1b1dff0 100644 >> --- a/arch/powerpc/kvm/book3s_hv.c >> +++ b/arch/powerpc/kvm/book3s_hv.c >> @@ -859,15 +859,9 @@ static int kvmppc_handle_exit_hv(struct kvm_run *run, >> struct kvm_vcpu *vcpu, >> r = RESUME_GUEST; >> break; >> case BOOK3S_INTERRUPT_MACHINE_CHECK: >> - /* >> - * Deliver a machine check interrupt to the guest. >> - * We have to do this, even if the host has handled the >> - * machine check, because machine checks use SRR0/1 and >> - * the interrupt might have trashed guest state in them. >> - */ >> - kvmppc_book3s_queue_irqprio(vcpu, >> - BOOK3S_INTERRUPT_MACHINE_CHECK); >> - r = RESUME_GUEST; >> + /* Exit to guest with KVM_EXIT_NMI as exit reason */ >> + run->exit_reason = KVM_EXIT_NMI; >> + r = RESUME_HOST; >> break; >> case BOOK3S_INTERRUPT_PROGRAM: >> { >> diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S >> b/arch/powerpc/kvm/book3s_hv_rmhandlers.S >> index b98889e..672b4f6 100644 >> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S >> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S >> @@ -147,7 +147,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S) >> addi r1, r1, 112 >> ld r7, HSTATE_HOST_MSR(r13) >> >> - cmpwi cr1, r12, BOOK3S_INTERRUPT_MACHINE_CHECK >> cmpwi r12, BOOK3S_INTERRUPT_EXTERNAL >> beq 11f >> cmpwi cr2, r12, BOOK3S_INTERRUPT_HMI >> @@ -160,7 +159,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S) >> mtmsrd r6, 1 /* Clear RI in MSR */ >> mtsrr0 r8 >> mtsrr1 r7 >> - beq cr1, 13f /* machine check */ >> RFI >> >> /* On POWER7, we have external interrupts set to use HSRR0/1 */ >> @@ -168,8 +166,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S) >> mtspr SPRN_HSRR1, r7 >> ba 0x500 >> >> -13: b machine_check_fwnmi >> - > > I don't quite understand the 3 hunks above. The rest seems to change > the delivery of MCs as I'd expect, but the above seems to change their > detection and the reason for that isn't obvious to me.
We need to do guest exit here and hence we continue with RFI or else if we branch to machine_check_fwnmi then the control will flow to opal_recover_mce routine without causing the guest to exit with NMI exit code. And I think, opal_recover_mce() is used to recover from UEs in host user/kernel space and does not have a check for UEs belonging to guest. Hence if we branch to machine_check_fwnmi we end up running into panic() in opal_machine_check() if UE belonged to guest. Regards, Aravinda > > >> 14: mtspr SPRN_HSRR0, r8 >> mtspr SPRN_HSRR1, r7 >> b hmi_exception_after_realmode >> @@ -2381,24 +2377,19 @@ machine_check_realmode: >> ld r9, HSTATE_KVM_VCPU(r13) >> li r12, BOOK3S_INTERRUPT_MACHINE_CHECK >> /* >> - * Deliver unhandled/fatal (e.g. UE) MCE errors to guest through >> - * machine check interrupt (set HSRR0 to 0x200). And for handled >> - * errors (no-fatal), just go back to guest execution with current >> - * HSRR0 instead of exiting guest. This new approach will inject >> - * machine check to guest for fatal error causing guest to crash. >> - * >> - * The old code used to return to host for unhandled errors which >> - * was causing guest to hang with soft lockups inside guest and >> - * makes it difficult to recover guest instance. >> + * Deliver unhandled/fatal (e.g. UE) MCE errors to guest >> + * by exiting the guest with KVM_EXIT_NMI exit reason (exit >> + * reason set later based on trap). For handled errors >> + * (no-fatal), go back to guest execution with current HSRR0 >> + * instead of exiting the guest. This approach will cause >> + * the guest to exit in case of fatal machine check error. >> */ >> - ld r10, VCPU_PC(r9) >> + bne 2f /* Continue guest execution? */ >> + /* If not, exit the guest. SRR0/1 are already set */ >> + b mc_cont >> +2: ld r10, VCPU_PC(r9) >> ld r11, VCPU_MSR(r9) >> - bne 2f /* Continue guest execution. */ >> - /* If not, deliver a machine check. SRR0/1 are already set */ >> - li r10, BOOK3S_INTERRUPT_MACHINE_CHECK >> - ld r11, VCPU_MSR(r9) >> - bl kvmppc_msr_interrupt >> -2: b fast_interrupt_c_return >> + b fast_interrupt_c_return >> >> /* >> * Check the reason we woke from nap, and take appropriate action. >> > -- Regards, Aravinda -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
