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

[Janosch Frank <frankja@linux.ibm.com>]

On 3/16/26 14:09, Christian Borntraeger wrote:
> 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;

We don't need to cast this to long anymore, do we?
Since sie_return is ulong, and we if we stay with positive numbers ulong 
would make the most sense.

Although I'd prefer a cast to stack_frame but I'm unsure if that would 
make it more readable if we stay with a one line change.

Rest looks good to me