[S390] s390-kvm: leave sie context on work. Removes preemption requirement
From: Martin Schwidefsky <schwidefsky@de.ibm.com>
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 <cotte@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/kernel/entry64.S b/arch/s390/kernel/entry64.S
index a57909d..fee1017 100644
--- a/arch/s390/kernel/entry64.S
+++ b/arch/s390/kernel/entry64.S
@@ -607,14 +607,37 @@
#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 @@
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
#
diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig
index 1761b74..e051cad 100644
--- a/arch/s390/kvm/Kconfig
+++ b/arch/s390/kvm/Kconfig
@@ -22,7 +22,6 @@
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
diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
index 349581a..47a0b64 100644
--- a/arch/s390/kvm/intercept.c
+++ b/arch/s390/kvm/intercept.c
@@ -105,6 +105,9 @@
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;
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 98d1e73..0ac36a6 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/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 @@
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)
diff --git a/include/asm-s390/kvm_host.h b/include/asm-s390/kvm_host.h
index f8204a4..18cbd8a 100644
--- a/include/asm-s390/kvm_host.h
+++ b/include/asm-s390/kvm_host.h
@@ -104,6 +104,7 @@
struct kvm_vcpu_stat {
u32 exit_userspace;
+ u32 exit_null;
u32 exit_external_request;
u32 exit_external_interrupt;
u32 exit_stop_request;