[PATCH v2] KVM: s390: vsie: Avoid injecting machine check on signal

[PATCH v2] KVM: s390: vsie: Avoid injecting machine check on signal

[Christian Borntraeger]

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.

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

 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               |  4 +++-
 7 files changed, 20 insertions(+), 14 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..1eb997335325 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -1178,11 +1178,13 @@ 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 (rc == SIE64_RETURN_MCCK) {
 		kvm_s390_reinject_machine_check(vcpu, &vsie_page->mcck_info);
 		return 0;
 	}
 
+	WARN_ON(rc != SIE64_RETURN_NORMAL);
+
 	if (rc > 0)
 		rc = 0; /* we could still have an icpt */
 	else if (current->thread.gmap_int_code)
-- 
2.53.0

Re: [PATCH v2] KVM: s390: vsie: Avoid injecting machine check on signal

[Christian Borntraeger]

Am 16.03.26 um 13:25 schrieb Christian Borntraeger:
> 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.
> 
> 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
> 
>   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               |  4 +++-
>   7 files changed, 20 insertions(+), 14 deletions(-)

I guess we should still add something like

--- 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_OK;
         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();
         }
@@ -1178,7 +1179,7 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page, struc
  
         kvm_vcpu_srcu_read_lock(vcpu);
  
-       if (rc == SIE64_RETURN_MCCK) {
+       if (sie_return == SIE64_RETURN_MCCK) {
                 kvm_s390_reinject_machine_check(vcpu, &vsie_page->mcck_info);
                 return 0;
         }

Re: [PATCH v2] KVM: s390: vsie: Avoid injecting machine check on signal

[Heiko Carstens]

On Mon, Mar 16, 2026 at 01:35:59PM +0100, Christian Borntraeger wrote:
> Am 16.03.26 um 13:25 schrieb Christian Borntraeger:
> I guess we should still add something like
> 
> --- 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_OK;
>         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();
>         }
> @@ -1178,7 +1179,7 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page, struc
>         kvm_vcpu_srcu_read_lock(vcpu);
> -       if (rc == SIE64_RETURN_MCCK) {
> +       if (sie_return == SIE64_RETURN_MCCK) {
>                 kvm_s390_reinject_machine_check(vcpu, &vsie_page->mcck_info);
>                 return 0;

Yes, this looks better and makes the code more understandable.

Re: [PATCH v2] KVM: s390: vsie: Avoid injecting machine check on signal

[Heiko Carstens]

On Mon, Mar 16, 2026 at 01:25:46PM +0100, Christian Borntraeger wrote:
>  	}
> +	WARN_ON(sie_return != SIE64_RETURN_NORMAL);

WARN_ON_ONCE() instead?

> +	WARN_ON(rc != SIE64_RETURN_NORMAL);
> +

Same here. Besides that looks good to me.