Commit f93d6d62 authored by Heiko Carstens's avatar Heiko Carstens
Browse files

KVM: s390: Increase size of union sca_utility to four bytes 



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.

Acked-by: default avatarClaudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: default avatarJanosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20241126102515.3178914-4-hca@linux.ibm.com


Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
parent 7061c639

arch/s390/include/asm/kvm_host.h

+10 −5
Original line number Diff line number Diff line
@@ -94,11 +94,16 @@ union ipte_control { 
	};

};



/*

 * Utility is defined as two bytes but having it four bytes wide

 * generates more efficient code. Since the following bytes are

 * reserved this makes no functional difference.

 */

union sca_utility {

	__u16 val;

	__u32 val;

	struct {

		__u16 mtcr : 1;

		__u16 reserved : 15;

		__u32 mtcr : 1;

		__u32	   : 31;

	};

};
@@ -107,7 +112,7 @@ 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 +120,7 @@ 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];