On Wed, Jan 13, 2016 at 12:38:09PM +0530, Aravinda Prasad wrote: > Enhance KVM to cause a guest exit with KVM_EXIT_NMI > exit reasons upon a machine check exception (MCE) in > the guest address space if the KVM_CAP_PPC_FWNMI > capability is enabled (instead of delivering 0x200 > interrupt to guest). This enables QEMU to build error > log and deliver machine check exception to guest via > guest registered machine check handler. > > 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 was enhanced to > patch 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: [snip] > --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S > +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S > @@ -133,21 +133,18 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S) > stb r0, HSTATE_HWTHREAD_REQ(r13) > > /* > - * For external and machine check interrupts, we need > - * to call the Linux handler to process the interrupt. > - * We do that by jumping to absolute address 0x500 for > - * external interrupts, or the machine_check_fwnmi label > - * for machine checks (since firmware might have patched > - * the vector area at 0x200). The [h]rfid at the end of the > - * handler will return to the book3s_hv_interrupts.S code. > - * For other interrupts we do the rfid to get back > - * to the book3s_hv_interrupts.S code here. > + * For external interrupts we need to call the Linux > + * handler to process the interrupt. We do that by jumping > + * to absolute address 0x500 for external interrupts. > + * The [h]rfid at the end of the handler will return to > + * the book3s_hv_interrupts.S code. For other interrupts > + * we do the rfid to get back to the book3s_hv_interrupts.S > + * code here. > */ > ld r8, 112+PPC_LR_STKOFF(r1) > 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 r12, BOOK3S_INTERRUPT_H_DOORBELL > @@ -162,7 +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 */ > @@ -170,8 +166,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S) > mtspr SPRN_HSRR1, r7 > ba 0x500 > > -13: b machine_check_fwnmi > - So, what you're disabling here is the host-side handling of the machine check after completing the guest->host switch. This has nothing to do with how the machine check gets communicated to the guest. Now, part of the host-side machine check handling has already happened, but I thought there was more that was done in host kernel virtual mode. If this change really is needed then I would want an ack from Mahesh that this is correct, and it will need to be explained in detail in the patch description. > 14: mtspr SPRN_HSRR0, r8 > mtspr SPRN_HSRR1, r7 > b hmi_exception_after_realmode > @@ -2390,15 +2384,13 @@ 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 either > + * through machine check interrupt (set HSRR0 to 0x200) or by > + * exiting the guest with KVM_EXIT_NMI exit reason if guest is > + * FWNMI capable. For handled errors (no-fatal), just go back > + * to guest execution with current HSRR0. This new approach > + * injects machine check errors in guest address space to guest > + * enabling guest kernel to suitably handle such errors. > * > * if we receive machine check with MSR(RI=0) then deliver it to > * guest as machine check causing guest to crash. > @@ -2408,11 +2400,17 @@ machine_check_realmode: > beq 1f /* Deliver a machine check to guest */ > ld r10, VCPU_PC(r9) > cmpdi r3, 0 /* Did we handle MCE ? */ > - bne 2f /* Continue guest execution. */ > + bne 3f /* Continue guest execution. */ > /* If not, deliver a machine check. SRR0/1 are already set */ > -1: li r10, BOOK3S_INTERRUPT_MACHINE_CHECK > +1: /* Check if guest is capable of handling NMI exit */ > + ld r3, VCPU_KVM(r9) Tab between opcode and first operand please, and also in the following lines. > + lbz r3, KVM_FWNMI(r3) > + cmpdi r3, 1 /* FWNMI capable? */ > + bne 2f > + b mc_cont Why not just beq mc_cont rather than the bne 2f; b mc_cont? > +2: li r10, BOOK3S_INTERRUPT_MACHINE_CHECK > bl kvmppc_msr_interrupt > -2: b fast_interrupt_c_return > +3: b fast_interrupt_c_return Paul. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
