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 <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: default avatarCarsten Otte <cotte@de.ibm.com>
Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 2688905e

arch/s390/kernel/entry64.S

+29 −1
Original line number Original line Diff line number Diff line
@@ -607,14 +607,37 @@ io_restore_trace_psw: 
#endif

#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:

io_work:

	tm	SP_PSW+1(%r15),0x01	# returning to user ?

	tm	SP_PSW+1(%r15),0x01	# returning to user ?

#ifndef CONFIG_PREEMPT

#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

	jno	io_restore		# no-> skip resched & signal

#endif

#else

#else

	jnz	io_work_user		# yes -> do 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)

0:

#endif

	# check for preemptive scheduling

	# check for preemptive scheduling

	icm	%r0,15,__TI_precount(%r9)

	icm	%r0,15,__TI_precount(%r9)

	jnz	io_restore		# preemption is disabled

	jnz	io_restore		# preemption is disabled
@@ -652,6 +675,11 @@ io_work_loop: 
	j	io_restore

	j	io_restore

io_work_done:

io_work_done:





#if defined(CONFIG_KVM) || defined(CONFIG_KVM_MODULE)

sie_opcode:

	.long 0xb2140000

#endif



#

#

# _TIF_MCCK_PENDING is set, call handler

# _TIF_MCCK_PENDING is set, call handler

#

#

arch/s390/kvm/Kconfig

+0 −1
Original line number Original line Diff line number Diff line
@@ -22,7 +22,6 @@ config KVM 
	select PREEMPT_NOTIFIERS

	select PREEMPT_NOTIFIERS

	select ANON_INODES

	select ANON_INODES

	select S390_SWITCH_AMODE

	select S390_SWITCH_AMODE

	select PREEMPT

	---help---

	---help---

	  Support hosting paravirtualized guest machines using the SIE

	  Support hosting paravirtualized guest machines using the SIE

	  virtualization capability on the mainframe. This should work

	  virtualization capability on the mainframe. This should work

arch/s390/kvm/intercept.c

+3 −0
Original line number Original line Diff line number Diff line
@@ -105,6 +105,9 @@ static intercept_handler_t instruction_handlers[256] = { 
static int handle_noop(struct kvm_vcpu *vcpu)

static int handle_noop(struct kvm_vcpu *vcpu)

{

{

	switch (vcpu->arch.sie_block->icptcode) {

	switch (vcpu->arch.sie_block->icptcode) {

	case 0x0:

		vcpu->stat.exit_null++;

		break;

	case 0x10:

	case 0x10:

		vcpu->stat.exit_external_request++;

		vcpu->stat.exit_external_request++;

		break;

		break;

arch/s390/kvm/kvm-s390.c

+1 −4
Original line number Original line Diff line number Diff line
@@ -31,6 +31,7 @@ 




struct kvm_stats_debugfs_item debugfs_entries[] = {

struct kvm_stats_debugfs_item debugfs_entries[] = {

	{ "userspace_handled", VCPU_STAT(exit_userspace) },

	{ "userspace_handled", VCPU_STAT(exit_userspace) },

	{ "exit_null", VCPU_STAT(exit_null) },

	{ "exit_validity", VCPU_STAT(exit_validity) },

	{ "exit_validity", VCPU_STAT(exit_validity) },

	{ "exit_stop_request", VCPU_STAT(exit_stop_request) },

	{ "exit_stop_request", VCPU_STAT(exit_stop_request) },

	{ "exit_external_request", VCPU_STAT(exit_external_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;

	vcpu->arch.guest_fpregs.fpc &= FPC_VALID_MASK;

	restore_fp_regs(&vcpu->arch.guest_fpregs);

	restore_fp_regs(&vcpu->arch.guest_fpregs);

	restore_access_regs(vcpu->arch.guest_acrs);

	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)

void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)

include/asm-s390/kvm_host.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -104,6 +104,7 @@ struct sie_block { 




struct kvm_vcpu_stat {

struct kvm_vcpu_stat {

	u32 exit_userspace;

	u32 exit_userspace;

	u32 exit_null;

	u32 exit_external_request;

	u32 exit_external_request;

	u32 exit_external_interrupt;

	u32 exit_external_interrupt;

	u32 exit_stop_request;

	u32 exit_stop_request;