[PATCH 3/3] KVM: s390: Increase size of union sca_utility to four bytes

Heiko Carstens
2024-11-25T11:50:48Z

kvm_s390_update_topology_change_report() modifies a single bit within
sca_utility using cmpxchg(). Given that the size of the sca_utility union
is two bytes this generates very inefficient code. Change the size to four
bytes, so better code can be generated.

Even though the size of sca_utility doesn't reflect architecture anymore
this seems to be the easiest and most pragmatic approach to avoid
inefficient code.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/include/asm/kvm_host.h | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 1cd8eaebd3c0..1cb1de232b9e 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -95,10 +95,10 @@ union ipte_control {
};

union sca_utility {
- __u16 val;
+ __u32 val;
struct {
- __u16 mtcr : 1;
- __u16 reserved : 15;
+ __u32 mtcr : 1;
+ __u32 : 31;
};
};

@@ -107,7 +107,7 @@ struct bsca_block {
__u64 reserved[5];
__u64 mcn;
union sca_utility utility;
- __u8 reserved2[6];
+ __u8 reserved2[4];
struct bsca_entry cpu[KVM_S390_BSCA_CPU_SLOTS];
};

@@ -115,7 +115,7 @@ struct esca_block {
union ipte_control ipte_control;
__u64 reserved1[6];
union sca_utility utility;
- __u8 reserved2[6];
+ __u8 reserved2[4];
__u64 mcn[4];
__u64 reserved3[20];
struct esca_entry cpu[KVM_S390_ESCA_CPU_SLOTS];
--
2.45.2