Commit 0eaeafa1 authored by Christian Borntraeger's avatar Christian Borntraeger Committed by Martin Schwidefsky
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[S390] s390-kvm: leave sie context on work. Removes preemption requirement

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

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: default avatarCarsten Otte <>
Signed-off-by: default avatarChristian Borntraeger <>
Signed-off-by: default avatarMartin Schwidefsky <>
parent 2688905e
......@@ -607,14 +607,37 @@ io_restore_trace_psw:
# 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
tm SP_PSW+1(%r15),0x01 # returning to user ?
#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
jno io_restore # no-> skip resched & signal
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)
# 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
#if defined(CONFIG_KVM) || defined(CONFIG_KVM_MODULE)
.long 0xb2140000
# _TIF_MCCK_PENDING is set, call handler
......@@ -22,7 +22,6 @@ config KVM
select S390_SWITCH_AMODE
select PREEMPT
Support hosting paravirtualized guest machines using the SIE
virtualization capability on the mainframe. This should work
......@@ -105,6 +105,9 @@ static intercept_handler_t instruction_handlers[256] = {
static int handle_noop(struct kvm_vcpu *vcpu)
switch (vcpu->arch.sie_block->icptcode) {
case 0x0:
case 0x10:
......@@ -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, int cpu)
vcpu->arch.guest_fpregs.fpc &= FPC_VALID_MASK;
if (signal_pending(current))
void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
......@@ -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;
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