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Message-Id: <20251126-s390-kvm-xfer-to-guest-work-v2-3-1b8767879235@linux.ibm.com>
Date: Wed, 26 Nov 2025 16:33:12 +1100
From: Andrew Donnellan <ajd@...ux.ibm.com>
To: kvm@...r.kernel.org, linux-s390@...r.kernel.org,
linux-kernel@...r.kernel.org,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Janosch Frank <frankja@...ux.ibm.com>,
Claudio Imbrenda <imbrenda@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Sven Schnelle <svens@...ux.ibm.com>
Cc: Nicholas Miehlbradt <nicholas@...ux.ibm.com>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Andy Lutomirski <luto@...nel.org>,
David Hildenbrand <david@...nel.org>
Subject: [PATCH v2 3/3] KVM: s390: Use generic VIRT_XFER_TO_GUEST_WORK
functions
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@...ux.ibm.com>
Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
Signed-off-by: Andrew Donnellan <ajd@...ux.ibm.com>
---
v2: if work is handled, recheck for outstanding work with interrupts
disabled before entering guest (Heiko)
The way I've implemented this, I do the check between vcpu_pre_run() and
entering the guest, and bail out of the loop if
kvm_xfer_to_guest_mode_handle_work() returns nonzero, without calling
vcpu_post_run(). My impression is that this is safe, but it does mean
there is an sie_enter vcpu event and trace event which isn't matched with
corresponding exit events. Is this a problem?
---
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 cae908d645501ef7eb4edbe87b8431f6499370a4..0ca9d6587243c98034d086c0ebd4ef085e504faf 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 3cad08662b3d80aaf6f5f8891fc08b383c3c44d4..34a4b8d112d4d2572336200feff04ea395fa70c6 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>
@@ -4788,9 +4789,6 @@ 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))
@@ -5095,12 +5093,12 @@ 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
@@ -5112,7 +5110,17 @@ 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);
@@ -5142,9 +5150,12 @@ 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 347268f89f2f186bea623a3adff7376cabc305b2..fb630fba822efadbdb959ed646b45f00e138898f 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
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