Commit 0eaeafa1 authored by Christian Borntraeger's avatar Christian Borntraeger Committed by Martin Schwidefsky
Browse files

[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 Diff line number Diff line
@@ -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

#

arch/s390/kvm/Kconfig

+0 −1
Original line number Diff line number Diff line
@@ -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

arch/s390/kvm/intercept.c

+3 −0
Original line number Diff line number Diff line
@@ -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:

		vcpu->stat.exit_null++;

		break;

	case 0x10:

		vcpu->stat.exit_external_request++;

		break;

arch/s390/kvm/kvm-s390.c

+1 −4
Original line number Diff line number Diff line
@@ -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;

	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)

include/asm-s390/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

CRA Git | Maintained and supported by SUSTech CRA and CCSE