From: Christian Borntraeger From: Martin Schwidefsky This patch fixes a bug with cpu bound guest on kvm-s390. Sometimes it was impossible to deliver a signal to a spinning guest. We used preemption as a circumvention. The preemption notifiers called vcpu_load, which checked for pending signals and triggered a host intercept. But even with preemption, a sigkill was not delivered immediately. This patch changes the low level host interrupt handler to check for the SIE instruction, if TIF_WORK is set. In that case we change the instruction pointer of the return PSW to rerun the vcpu_run loop. The kvm code sees an intercept reason 0 if that happens. This patch adds accounting for these types of intercept as well. The advantages: - works with and without preemption - signals are delivered immediately - much better host latencies without preemption Acked-by: Carsten Otte Signed-off-by: Christian Borntraeger Signed-off-by: Martin Schwidefsky --- arch/s390/kernel/entry64.S | 30 +++++++++++++++++++++++++++++- arch/s390/kvm/Kconfig | 1 - arch/s390/kvm/intercept.c | 3 +++ arch/s390/kvm/kvm-s390.c | 5 +---- include/asm-s390/kvm_host.h | 1 + 5 files changed, 34 insertions(+), 6 deletions(-) Index: quilt-2.6/arch/s390/kernel/entry64.S =================================================================== --- quilt-2.6.orig/arch/s390/kernel/entry64.S +++ quilt-2.6/arch/s390/kernel/entry64.S @@ -607,14 +607,37 @@ io_restore_trace_psw: #endif # -# switch to kernel stack, then check TIF bits +# There is work todo, we need to check if we return to userspace, then +# check, if we are in SIE, if yes leave it # io_work: tm SP_PSW+1(%r15),0x01 # returning to user ? #ifndef CONFIG_PREEMPT +#if defined(CONFIG_KVM) || defined(CONFIG_KVM_MODULE) + jnz io_work_user # yes -> no need to check for SIE + la %r1, BASED(sie_opcode) # we return to kernel here + lg %r2, SP_PSW+8(%r15) + clc 0(2,%r1), 0(%r2) # is current instruction = SIE? + jne io_restore # no-> return to kernel + lg %r1, SP_PSW+8(%r15) # yes-> add 4 bytes to leave SIE + aghi %r1, 4 + stg %r1, SP_PSW+8(%r15) + j io_restore # return to kernel +#else jno io_restore # no-> skip resched & signal +#endif #else jnz io_work_user # yes -> do resched & signal +#if defined(CONFIG_KVM) || defined(CONFIG_KVM_MODULE) + la %r1, BASED(sie_opcode) + lg %r2, SP_PSW+8(%r15) + clc 0(2,%r1), 0(%r2) # is current instruction = SIE? + jne 0f # no -> leave PSW alone + lg %r1, SP_PSW+8(%r15) # yes-> add 4 bytes to leave SIE + aghi %r1, 4 + stg %r1, SP_PSW+8(%r15) +0: +#endif # check for preemptive scheduling icm %r0,15,__TI_precount(%r9) jnz io_restore # preemption is disabled @@ -652,6 +675,11 @@ io_work_loop: j io_restore io_work_done: +#if defined(CONFIG_KVM) || defined(CONFIG_KVM_MODULE) +sie_opcode: + .long 0xb2140000 +#endif + # # _TIF_MCCK_PENDING is set, call handler # Index: quilt-2.6/arch/s390/kvm/intercept.c =================================================================== --- quilt-2.6.orig/arch/s390/kvm/intercept.c +++ quilt-2.6/arch/s390/kvm/intercept.c @@ -105,6 +105,9 @@ static intercept_handler_t instruction_h static int handle_noop(struct kvm_vcpu *vcpu) { switch (vcpu->arch.sie_block->icptcode) { + case 0x0: + vcpu->stat.exit_null++; + break; case 0x10: vcpu->stat.exit_external_request++; break; Index: quilt-2.6/arch/s390/kvm/Kconfig =================================================================== --- quilt-2.6.orig/arch/s390/kvm/Kconfig +++ quilt-2.6/arch/s390/kvm/Kconfig @@ -22,7 +22,6 @@ config KVM select PREEMPT_NOTIFIERS select ANON_INODES select S390_SWITCH_AMODE - select PREEMPT ---help--- Support hosting paravirtualized guest machines using the SIE virtualization capability on the mainframe. This should work Index: quilt-2.6/arch/s390/kvm/kvm-s390.c =================================================================== --- quilt-2.6.orig/arch/s390/kvm/kvm-s390.c +++ quilt-2.6/arch/s390/kvm/kvm-s390.c @@ -31,6 +31,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = { { "userspace_handled", VCPU_STAT(exit_userspace) }, + { "exit_null", VCPU_STAT(exit_null) }, { "exit_validity", VCPU_STAT(exit_validity) }, { "exit_stop_request", VCPU_STAT(exit_stop_request) }, { "exit_external_request", VCPU_STAT(exit_external_request) }, @@ -221,10 +222,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu vcpu->arch.guest_fpregs.fpc &= FPC_VALID_MASK; restore_fp_regs(&vcpu->arch.guest_fpregs); restore_access_regs(vcpu->arch.guest_acrs); - - if (signal_pending(current)) - atomic_set_mask(CPUSTAT_STOP_INT, - &vcpu->arch.sie_block->cpuflags); } void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) Index: quilt-2.6/include/asm-s390/kvm_host.h =================================================================== --- quilt-2.6.orig/include/asm-s390/kvm_host.h +++ quilt-2.6/include/asm-s390/kvm_host.h @@ -104,6 +104,7 @@ struct sie_block { struct kvm_vcpu_stat { u32 exit_userspace; + u32 exit_null; u32 exit_external_request; u32 exit_external_interrupt; u32 exit_stop_request; -- blue skies, Martin. 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