[PATCH v3] KVM: s390: vsie: Avoid injecting machine check on signal

Christian Borntraeger
2026-03-16T13:09:57Z

The recent XFER_TO_GUEST_WORK change resulted in a situation, where the
vsie code would interpret a signal during work as a machine check during
SIE as both use the EINTR return code.
The exit_reason of the sie64a function has nothing to do with the
kvm_run exit_reason. Rename it and define a specific code for machine
checks instead of abusing -EINTR.
rename exit_reason into sie_return to avoid the naming conflict
and change the code flow in vsie.c to have a separate variable for rc
and sie_return.

Fixes: 2bd1337a1295e ("KVM: s390: Use generic VIRT_XFER_TO_GUEST_WORK functions")
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
---
v1->v2:
instead of a band-aid, make the machine check more direct
v2->v3:
avoid overloading the rc variable in vsie.c

arch/s390/include/asm/kvm_host.h | 3 +++
arch/s390/include/asm/stacktrace.h | 2 +-
arch/s390/kernel/asm-offsets.c | 2 +-
arch/s390/kernel/entry.S | 4 ++--
arch/s390/kernel/nmi.c | 4 ++--
arch/s390/kvm/kvm-s390.c | 15 ++++++++-------
arch/s390/kvm/vsie.c | 7 +++++--
7 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 64a50f0862aa..3039c88daa63 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -710,6 +710,9 @@ void kvm_arch_crypto_clear_masks(struct kvm *kvm);
void kvm_arch_crypto_set_masks(struct kvm *kvm, unsigned long *apm,
unsigned long *aqm, unsigned long *adm);

+#define SIE64_RETURN_NORMAL 0
+#define SIE64_RETURN_MCCK 1
+
int __sie64a(phys_addr_t sie_block_phys, struct kvm_s390_sie_block *sie_block, u64 *rsa,
unsigned long gasce);

diff --git a/arch/s390/include/asm/stacktrace.h b/arch/s390/include/asm/stacktrace.h
index c9ae680a28af..ac3606c3babe 100644
--- a/arch/s390/include/asm/stacktrace.h
+++ b/arch/s390/include/asm/stacktrace.h
@@ -62,7 +62,7 @@ struct stack_frame {
struct {
unsigned long sie_control_block;
unsigned long sie_savearea;
- unsigned long sie_reason;
+ unsigned long sie_return;
unsigned long sie_flags;
unsigned long sie_control_block_phys;
unsigned long sie_guest_asce;
diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
index e1a5b5b54e4f..fbd26f3e9f96 100644
--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -63,7 +63,7 @@ int main(void)
OFFSET(__SF_EMPTY, stack_frame, empty[0]);
OFFSET(__SF_SIE_CONTROL, stack_frame, sie_control_block);
OFFSET(__SF_SIE_SAVEAREA, stack_frame, sie_savearea);
- OFFSET(__SF_SIE_REASON, stack_frame, sie_reason);
+ OFFSET(__SF_SIE_RETURN, stack_frame, sie_return);
OFFSET(__SF_SIE_FLAGS, stack_frame, sie_flags);
OFFSET(__SF_SIE_CONTROL_PHYS, stack_frame, sie_control_block_phys);
OFFSET(__SF_SIE_GUEST_ASCE, stack_frame, sie_guest_asce);
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 4873fe9d891b..5817cb47b2d0 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -200,7 +200,7 @@ SYM_FUNC_START(__sie64a)
stg %r3,__SF_SIE_CONTROL(%r15) # ...and virtual addresses
stg %r4,__SF_SIE_SAVEAREA(%r15) # save guest register save area
stg %r5,__SF_SIE_GUEST_ASCE(%r15) # save guest asce
- xc __SF_SIE_REASON(8,%r15),__SF_SIE_REASON(%r15) # reason code = 0
+ xc __SF_SIE_RETURN(8,%r15),__SF_SIE_RETURN(%r15) # return code = 0
mvc __SF_SIE_FLAGS(8,%r15),__TI_flags(%r14) # copy thread flags
lmg %r0,%r13,0(%r4) # load guest gprs 0-13
mvi __TI_sie(%r14),1
@@ -237,7 +237,7 @@ SYM_INNER_LABEL(sie_exit, SYM_L_GLOBAL)
xgr %r4,%r4
xgr %r5,%r5
lmg %r6,%r14,__SF_GPRS(%r15) # restore kernel registers
- lg %r2,__SF_SIE_REASON(%r15) # return exit reason code
+ lg %r2,__SF_SIE_RETURN(%r15) # return sie return code
BR_EX %r14
SYM_FUNC_END(__sie64a)
EXPORT_SYMBOL(__sie64a)
diff --git a/arch/s390/kernel/nmi.c b/arch/s390/kernel/nmi.c
index a55abbf65333..fc1f775e4517 100644
--- a/arch/s390/kernel/nmi.c
+++ b/arch/s390/kernel/nmi.c
@@ -487,8 +487,8 @@ void notrace s390_do_machine_check(struct pt_regs *regs)
mcck_dam_code = (mci.val & MCIC_SUBCLASS_MASK);
if (test_cpu_flag(CIF_MCCK_GUEST) &&
(mcck_dam_code & MCCK_CODE_NO_GUEST) != mcck_dam_code) {
- /* Set exit reason code for host's later handling */
- *((long *)(regs->gprs[15] + __SF_SIE_REASON)) = -EINTR;
+ /* Set sie return code for host's later handling */
+ *((long *)(regs->gprs[15] + __SF_SIE_RETURN)) = SIE64_RETURN_MCCK;
}
clear_cpu_flag(CIF_MCCK_GUEST);

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 1668580008c6..b93722b57d1c 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -4617,7 +4617,7 @@ static int vcpu_post_run_handle_fault(struct kvm_vcpu *vcpu)
return 0;
}

-static int vcpu_post_run(struct kvm_vcpu *vcpu, int exit_reason)
+static int vcpu_post_run(struct kvm_vcpu *vcpu, int sie_return)
{
struct mcck_volatile_info *mcck_info;
struct sie_page *sie_page;
@@ -4633,13 +4633,14 @@ static int vcpu_post_run(struct kvm_vcpu *vcpu, int exit_reason)
vcpu->run->s.regs.gprs[14] = vcpu->arch.sie_block->gg14;
vcpu->run->s.regs.gprs[15] = vcpu->arch.sie_block->gg15;

- if (exit_reason == -EINTR) {
+ if (sie_return == SIE64_RETURN_MCCK) {
sie_page = container_of(vcpu->arch.sie_block,
struct sie_page, sie_block);
mcck_info = &sie_page->mcck_info;
kvm_s390_reinject_machine_check(vcpu, mcck_info);
return 0;
}
+ WARN_ON(sie_return != SIE64_RETURN_NORMAL);

if (vcpu->arch.sie_block->icptcode > 0) {
rc = kvm_handle_sie_intercept(vcpu);
@@ -4678,7 +4679,7 @@ int noinstr kvm_s390_enter_exit_sie(struct kvm_s390_sie_block *scb,
#define PSW_INT_MASK (PSW_MASK_EXT | PSW_MASK_IO | PSW_MASK_MCHECK)
static int __vcpu_run(struct kvm_vcpu *vcpu)
{
- int rc, exit_reason;
+ int rc, sie_return;
struct sie_page *sie_page = (struct sie_page *)vcpu->arch.sie_block;

/*
@@ -4718,9 +4719,9 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
guest_timing_enter_irqoff();
__disable_cpu_timer_accounting(vcpu);

- exit_reason = kvm_s390_enter_exit_sie(vcpu->arch.sie_block,
- vcpu->run->s.regs.gprs,
- vcpu->arch.gmap->asce.val);
+ sie_return = kvm_s390_enter_exit_sie(vcpu->arch.sie_block,
+ vcpu->run->s.regs.gprs,
+ vcpu->arch.gmap->asce.val);

__enable_cpu_timer_accounting(vcpu);
guest_timing_exit_irqoff();
@@ -4743,7 +4744,7 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
}
kvm_vcpu_srcu_read_lock(vcpu);

- rc = vcpu_post_run(vcpu, exit_reason);
+ rc = vcpu_post_run(vcpu, sie_return);
if (rc || guestdbg_exit_pending(vcpu)) {
kvm_vcpu_srcu_read_unlock(vcpu);
break;
diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index c0d36afd4023..42c53134e0b8 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -1123,6 +1123,7 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page, struc
struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
struct kvm_s390_sie_block *scb_o = vsie_page->scb_o;
int guest_bp_isolation;
+ int sie_return = SIE64_RETURN_NORMAL;
int rc = 0;

handle_last_fault(vcpu, vsie_page, sg);
@@ -1163,7 +1164,7 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page, struc
goto xfer_to_guest_mode_check;
}
guest_timing_enter_irqoff();
- rc = kvm_s390_enter_exit_sie(scb_s, vcpu->run->s.regs.gprs, sg->asce.val);
+ sie_return = kvm_s390_enter_exit_sie(scb_s, vcpu->run->s.regs.gprs, sg->asce.val);
guest_timing_exit_irqoff();
local_irq_enable();
}
@@ -1178,11 +1179,13 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page, struc

kvm_vcpu_srcu_read_lock(vcpu);

- if (rc == -EINTR) {
+ if (sie_return == SIE64_RETURN_MCCK) {
kvm_s390_reinject_machine_check(vcpu, &vsie_page->mcck_info);
return 0;
}

+ WARN_ON(sie_return != SIE64_RETURN_NORMAL);
+
if (rc > 0)
rc = 0; /* we could still have an icpt */
else if (current->thread.gmap_int_code)
--
2.53.0