[GIT PULL 10/10] KVM: s390: Use generic VIRT_XFER_TO_GUEST_WORK functions

Janosch Frank
2025-12-01T12:45:21Z

From: Andrew Donnellan <ajd@linux.ibm.com>

Switch to using the generic infrastructure to check for and handle pending
work before transitioning into guest mode.

xfer_to_guest_mode_handle_work() does a few more things than the current
code does when deciding whether or not to exit the __vcpu_run() loop. The
exittime tests from kvm-unit-tests, in my tests, were within a few percent
compared to before this series, which is within noise tolerance.

Co-developed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
[frankja@linux.ibm.com: Removed semicolon]
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
---
arch/s390/kvm/Kconfig | 1 +
arch/s390/kvm/kvm-s390.c | 25 ++++++++++++++++++-------
arch/s390/kvm/vsie.c | 18 +++++++++++++-----
3 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig
index cae908d64550..0ca9d6587243 100644
--- a/arch/s390/kvm/Kconfig
+++ b/arch/s390/kvm/Kconfig
@@ -30,6 +30,7 @@ config KVM
select HAVE_KVM_NO_POLL
select KVM_VFIO
select MMU_NOTIFIER
+ select VIRT_XFER_TO_GUEST_WORK
help
Support hosting paravirtualized guest machines using the SIE
virtualization capability on the mainframe. This should work
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 4d13601ec217..d31155e371df 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -14,6 +14,7 @@
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/compiler.h>
+#include <linux/entry-virt.h>
#include <linux/export.h>
#include <linux/err.h>
#include <linux/fs.h>
@@ -4675,9 +4676,6 @@ static int vcpu_pre_run(struct kvm_vcpu *vcpu)
vcpu->arch.sie_block->gg14 = vcpu->run->s.regs.gprs[14];
vcpu->arch.sie_block->gg15 = vcpu->run->s.regs.gprs[15];

- if (need_resched())
- schedule();
-
if (!kvm_is_ucontrol(vcpu->kvm)) {
rc = kvm_s390_deliver_pending_interrupts(vcpu);
if (rc || guestdbg_exit_pending(vcpu))
@@ -4982,12 +4980,12 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
*/
kvm_vcpu_srcu_read_lock(vcpu);

- do {
+ while (true) {
rc = vcpu_pre_run(vcpu);
+ kvm_vcpu_srcu_read_unlock(vcpu);
if (rc || guestdbg_exit_pending(vcpu))
break;

- kvm_vcpu_srcu_read_unlock(vcpu);
/*
* As PF_VCPU will be used in fault handler, between
* guest_timing_enter_irqoff and guest_timing_exit_irqoff
@@ -4999,7 +4997,17 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
sizeof(sie_page->pv_grregs));
}

+xfer_to_guest_mode_check:
local_irq_disable();
+ xfer_to_guest_mode_prepare();
+ if (xfer_to_guest_mode_work_pending()) {
+ local_irq_enable();
+ rc = kvm_xfer_to_guest_mode_handle_work(vcpu);
+ if (rc)
+ break;
+ goto xfer_to_guest_mode_check;
+ }
+
guest_timing_enter_irqoff();
__disable_cpu_timer_accounting(vcpu);

@@ -5029,9 +5037,12 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
kvm_vcpu_srcu_read_lock(vcpu);

rc = vcpu_post_run(vcpu, exit_reason);
- } while (!signal_pending(current) && !guestdbg_exit_pending(vcpu) && !rc);
+ if (rc || guestdbg_exit_pending(vcpu)) {
+ kvm_vcpu_srcu_read_unlock(vcpu);
+ break;
+ }
+ }

- kvm_vcpu_srcu_read_unlock(vcpu);
return rc;
}

diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index d23ab5120888..b526621d2a1b 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -1180,12 +1180,23 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
current->thread.gmap_int_code = 0;
barrier();
if (!kvm_s390_vcpu_sie_inhibited(vcpu)) {
+xfer_to_guest_mode_check:
local_irq_disable();
+ xfer_to_guest_mode_prepare();
+ if (xfer_to_guest_mode_work_pending()) {
+ local_irq_enable();
+ rc = kvm_xfer_to_guest_mode_handle_work(vcpu);
+ if (rc)
+ goto skip_sie;
+ goto xfer_to_guest_mode_check;
+ }
guest_timing_enter_irqoff();
rc = kvm_s390_enter_exit_sie(scb_s, vcpu->run->s.regs.gprs, vsie_page->gmap->asce);
guest_timing_exit_irqoff();
local_irq_enable();
}
+
+skip_sie:
barrier();
vcpu->arch.sie_block->prog0c &= ~PROG_IN_SIE;

@@ -1345,13 +1356,11 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
* but rewind the PSW to re-enter SIE once that's completed
* instead of passing a "no action" intercept to the guest.
*/
- if (signal_pending(current) ||
- kvm_s390_vcpu_has_irq(vcpu, 0) ||
+ if (kvm_s390_vcpu_has_irq(vcpu, 0) ||
kvm_s390_vcpu_sie_inhibited(vcpu)) {
kvm_s390_rewind_psw(vcpu, 4);
break;
}
- cond_resched();
}

if (rc == -EFAULT) {
@@ -1483,8 +1492,7 @@ int kvm_s390_handle_vsie(struct kvm_vcpu *vcpu)
if (unlikely(scb_addr & 0x1ffUL))
return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);

- if (signal_pending(current) || kvm_s390_vcpu_has_irq(vcpu, 0) ||
- kvm_s390_vcpu_sie_inhibited(vcpu)) {
+ if (kvm_s390_vcpu_has_irq(vcpu, 0) || kvm_s390_vcpu_sie_inhibited(vcpu)) {
kvm_s390_rewind_psw(vcpu, 4);
return 0;
}
--
2.52.0